Method and apparatus for charging a battery

ABSTRACT

A battery is charged by repeatedly alternating between test and charge cycles. During the test cycle, the dynamic voltage-current characteristic of the battery is obtained as a function of the charge condition of the battery. During the charge cycle, a gradually varying voltage is supplied to the battery, substantially without controlling the current supplied thereto, for a predetermined time. The rate at which this supplied voltage varies is related to the dynamic voltage-current characteristic obtained during the test cycle. Alternating between test and charge cycles continues until the dynamic voltage-current characteristic last obtained is substantially identical to the preceding dynamic voltage-current characteristic, whereupon the charging of the battery is terminated.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for charging a battery,such as an industrial battery, and more particularly, to such a methodand apparatus whereby the battery is charged quickly and accurately tothe proper charge level. The apparatus described herein is referred toas a "smart" battery charger.

Typical industrial-type batteries, sometimes referred to as "traction"batteries, are used commonly to drive motor vehicles in factories,warehouses, and the like. In such industrial applications, it isnecessary that batteries whose charges have been depleted be quicklyre-charged for subsequent re-use. Such batteries exhibit high chargecapacities, on the order of several hundred ampere-hours (A.H.), andusually are acid-type batteries, such as the conventional lead-acidbattery. Desirably, such industrial batteries should be charged byapparatus that is relatively simple to operate.

A typical lead-acid battery, when charged above a predetermined level,exhibits a "gassing" condition, wherein the electrolyte is sufficientlyagitated so as to emit gas. In many commercially available batterychargers, energy is supplied to charge the battery until the gassingcondition is attained, and charging then continues for a predeterminedtime after the onset of this condition. Thereafter, an "equalizing"charge is supplied to the battery to balance inherent losses therein. Toavoid damage to the battery, when the gassing level is attained, as whena substantially discharged battery is charged, the current suppliedduring the gas period should be relatively low. Some chargers supplyconstant charging currents for a pre-set time duration. Depending uponthis overall charge time duration, the charging current is establishedaccordingly. For example, a predetermined percentage of the ratedbattery capacity (A.H.) is supplied for the charge duration; and thispercentage is inversely related to the overall charging time. Hence, ifthe battery is to be charged over a substantially long duration, a lowcharge current level is used. Conversely, if the battery is to becharged over a relatively short duration, a higher charge current levelis supplied. This suffers from the disadvantage of supplying either toohigh a current during the gassing period, thereby resulting in damage tothe battery, or too low a current such that the battery is notsatisfactorily charged to its proper level.

Other battery chargers employ the so-called constant voltage techniquewherein a constant charging voltage is applied across the battery forthe pre-set charging duration. However, this technique does not takeinto account a change in the actual charge capacity of the battery dueto repeated charging operations and, thus, becomes less effective as thebattery ages.

Another disadvantage of commercially available battery chargers is thatmany establish a pre-set charging time which, generally, is unrelated tothe actual charge level of the battery. The battery then is charged witha substantially constant charging current which is established by theoperator as a function of the rated battery capacity. Since, over aperiod of time, the actual battery capacity may differ substantiallyfrom its rated capacity, the charging current might be too high. Also,if the battery exhibits a relatively low charge level, the charging timeduration may be insufficient to charge the battery satisfactorily.

A battery charger has been introduced by Christie Electric Corp., LosAngeles, California, which charges the battery by interspersingnegative, or discharge, pulses during the charging operation; with thenumber of negative pulses being a function of battery capacity. Thestate-of-charge of the battery is measured by, for example, an ammeter,which indicates battery current during the negative pulse duration, andthis negative pulse duration is increased as the state-of-chargeincreases. However, this charger suffers from many of the aforenoteddisadvantages, such as operating over a pre-set charging time durationwhich may be too short or too long. Also, this charger operates withrelatively low capacity batteries.

A battery charger introduced by Westinghouse Davenset Rectifiers ofEngland supplies a charging current to the battery and senses when thebattery voltage reaches a predetermined level. This level is assumed tobe the gas voltage (V_(gas)) level, whereupon a pre-set timer istriggered to establish the gas period. At the termination of thispre-set gas period, normal charging is terminated; and the battery thenis supplied with an equalizing charge followed by a "hold ready" chargewhich replaces open circuit losses. While this charger includes variousfeatures, such as pre-gas charge protection, avoiding the establishmentof the gas period if a fully charged or slightly discharged battery isused, charging nevertheless occurs during a pre-set time interval. Thereis little, if any, correlation between the actual state-of-charge of thebattery and the charging duration. Hence, this charger may, undesirably,either over-charge or under-charge a battery connected thereto.

In the battery charger manufactured by Oldham/Harmer & Simmons, ofEngland, a charging current is supplied to the battery, and this currentis measured for a brief period of time when the battery voltage reachesits gas voltage level V_(gas). This sequencing between charging andmeasuring cycles continues until the amount of measured current in twosuccessive measuring cycles is equal. At that point, the battery isconsidered fully charged. Thereafter, a low level of equalizing chargeis supplied. This charger, however, operates substantially independentlyof the actual condition of the battery. Although the charging cycle isterminated when two successive current measurements are equal, this doesnot necessarily mean that the battery has been fully charged.Furthermore, the charging current levels are dependent upon the ratedbattery capacity; which may differ substantially from the actualcapacity thereof. Another disadvantage of this charger, which is commonwith the aforementioned chargers, is that actual battery operating andfault conditions are not sensed automatically or indicated to anoperator. Hence, faulty or defective batteries may be charged, with aresultant waste in energy and time. Furthermore, a faulty battery, whichmay be easily repaired, if not indicated, may be supplied with acharging current that results in permanent damage.

It also has been proposed by the prior art to supply a charging currentto a battery, and to interrupt the charging current periodically tomeasure the battery voltage. This measure of battery voltage is used toindicate whether the battery has reached its gassing level, and thecharging current magnitude is reduced when this gassing level isattained. Although the battery voltage is "tested" periodically, suchtests are not used to indicate the condition of the battery, nor are thetest results used to indicate when the battery has been satisfactorilycharged.

The prior art also has proposed a battery test arrangement wherein acurrent ramp is supplied, resulting in a change in the battery voltage.The voltage-current characteristic for each cell, which is a function ofthe supplied current and measured voltage, is determined by a computer;and an average voltage-current characteristic is derived from all of thecells. Then, the voltage-current characteristic of each cell is comparedto the average voltage-current characteristic, and the battery isrejected if the characteristic of any one cell differs significantlyfrom the average characteristic. However, this arrangement requiresdirect access to each cell of the battery. In many industrial batteries,such access is difficult, if not impossible. Furthermore, since thebattery is "tested" by deriving an average voltage-currentcharacteristic therefrom, a battery which is severely defective will notbe detected. Still further, although this prior art proposal describes abattery test technique, that technique is not used to control a batterycharging operation.

Yet another prior art battery test technique proposes that avoltage-current curve derived from the tested battery be plotted, andthat the slope of this curve be compared to an "average" curve whichrepresents average slopes for different battery charge levels. Then, theactual charge level of the battery under test is determined by notingthe charge level on this "average" curve corresponding to the measuredslope of the test voltage-current curve. Here too, however, the batterytest technique is not used to control a charging operation. Furthermore,this test technique, although helpful in obtaining a measure of thestate-of-charge of the battery, nevertheless does not provideindications of various fault conditions which may exist.

Another problem associated with many battery chargers is that thecharging current supplied thereby should be matched to the battery whichis charged. Typically, it is necessary that the capacity of the batteryas well as the number of cells included therein be known in advance.Furthermore, many of these chargers will attempt to charge a defectivebattery notwithstanding a serious fault condition which may be present.This can result in damage to the battery as well as produce a hazardouscondition.

Therefore, there has been a need for a battery charger apparatus whichoperates substantially automatically, requiring little, if any, advanceinformation concerning the battery capacity, number of cells, and thelike. There also has been a need for a battery charger of relativelysmall size and light weight. Such a charger, desirably, should becapable of testing the condition of the battery and indicate, ordisplay, various fault conditions. Such a charger also should becapable, advantageously, of controlling the charging operation as afunction of the instantaneous condition of the battery, and to terminatethe charging operation when the battery is fully charged, regardless ofthe time duration required to attain such a fully-charged state.

OBJECTS OF THE INVENTION

Therefore, it is an object of the present invention to provide animproved method and apparatus for charging a battery which overcomes theaforenoted disadvantages attending prior art techniques.

Another object of this invention is to provide a method and apparatusfor charging a battery, wherein the battery is quickly and accuratelycharged to its full capacity.

A further object of this invention is to provide a method and apparatusfor charging a battery wherein detailed information relating to thatbattery, such as number of cells, charge capacity, presentstate-of-charge, and the like, need not be known in advance.

An additional object of this invention is to provide a method andapparatus for charging a battery wherein the condition of the battery istested to detect a possible fault condition prior to charging thereof.

Yet another object of this invention is to provide a method andapparatus for charging a battery wherein, during the charging operation,a test cycle is carried out periodically, the results of this test cycleserving to indicate the condition of the battery so as to control thecharging cycle.

A still further object of this invention is to provide a method andapparatus for charging a battery wherein test cycles and charge cyclesare carried out repeatedly and alternately, a dynamic voltage-currentcharacteristic of the battery being obtained during the test cycles, andthe charging operation being terminated when successive voltage-currentcharacteristics are substantially identical.

Various other objects, advantages and features of the present inventionwill become readily apparent from the ensuing detailed description, andthe novel features will be particularly pointed out in the appendedclaims.

SUMMARY OF THE INVENTION

In accordance with this invention, a method and apparatus are providedfor charging a battery by repeatedly alternating between test and chargecycles. During the test cycle, the dynamic voltage-currentcharacteristic of the battery is obtained as a function of the chargecondition thereof. During the charge cycle, a gradually varying voltageis supplied to the battery, substantially without controlling thecurrent supplied thereto, for a predetermined time. The rate at whichthis voltage varies is related to the dynamic voltage-currentcharacteristic obtained during the test cycle. Alternating between testand charge cycles continues until the dynamic voltage-currentcharacteristic last obtained is substantially identical to the precedingdynamic voltage-current characteristic, whereupon the charging of thebattery is terminated.

In accordance with one aspect of this invention, the dynamicvoltage-current characteristic of the battery is obtained by supplying acontrollably varying charging current, such as an increasing rampcurrent followed by a decreasing ramp current, to the battery; andmeasuring the voltage produced across the battery output terminals inresponse to the charging current supplied thereto while that chargingcurrent is being supplied. As a feature of this invention, theincreasing and decreasing current ramps are separated by a duration ofsubstantially constant current of a magnitude sufficient to induceinternal bubbling of the battery. In a preferred embodiment, a dataprocessor, such as a microprocessor, is used to control the chargingcurrent that is supplied to the battery.

In accordance with another aspect of this invention, various conditionsof the battery are determined as a function of the dynamicvoltage-current characteristic which is obtained. For example,discontinuities in the slope of the voltage-current characteristicoccurring at certain voltage levels may indicate a fault condition. Asanother example, the slope of the voltage-current characteristic mayprovide a reasonably accurate representation of the actual chargecapacity of the battery. As a further example, the so-calledopen-circuit voltage, that is, the voltage obtained on a voltage-currentcharacteristic when the battery current is substantially equal to zero,provides a reasonably accurate representation of the state-of-charge ofthe battery.

As yet another aspect of this invention, the charging cycle is carriedout by supplying a ramp voltage to the battery. The slope of this rampvoltage is controlled as a function of the state-of-charge. Preferably,this ramp voltage exhibits a relatively steeper slope until the batteryis charged to its gassing level, and thereafter, the slope of the rampvoltage is reduced.

As a further feature of this invention, the occurrence ofdiscontinuities in the slope of the voltage-current characteristic isdetected, and when such discontinuities occur in response tosubstantially the same charging current level during successive testcycles, it is concluded that the battery has been charged to itscapacity.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example, will bestbe understood in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of apparatus capable of carrying out thepresent invention;

FIGS. 2A-2D are graphical representations of the voltage-currentcharacteristics which are obtained for a battery being charged todifferent states-of-charge;

FIG. 3 is a block diagram of a preferred embodiment of the presentinvention;

FIG. 4 is a block diagram of a portion of the apparatus shown in FIG. 3;

FIG. 5 is a flow chart of a general program which can be used by a dataprocessor to carry out the present invention;

FIG. 6 is a waveform diagram of the charging voltage which is used inaccordance with the present invention;

FIGS. 7A-7B comprise a flow chart representing a test cycle routinecarried out by the data processor which is used with the presentinvention; and

FIG. 8 is a waveform of the charging current that is supplied during thetest cycle of the present invention.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals are used,FIG. 1 is a block diagram of one embodiment of apparatus which can beused to charge a battery 10. The illustrated apparatus is adapted tocharge various types of secondary cells; and the following discussion isdirected to charging apparatus which is particularly adapted to chargean acid-type industrial battery, such as a lead acid battery.Preferably, battery 10 is formed of a plurality of cascaded cells, suchthat the output voltage produced by that battery, that is, the outputvoltage which appears across the battery terminals, is a function of thenumber of cells included therein. Typically, each cell produces avoltage on the order of about 2 volts, the actual cell voltage being afunction of its state-of-charge. As a numerical example, a "normal"fully-charged battery produces an output voltage of about 2.2 volts.This cell voltage is less for lesser states-of-charge. Accordingly, fora 6-cell battery, the output battery voltage normally can be expected torange between 12.0 volts and 13.2 volts, with the actual battery voltagebeing a function of the charge condition thereof.

The apparatus illustrated in FIG. 1 is comprised of a variable currentsource 12, a voltage source 14, a selector switch 16, a power outputcircuit 18 and a graphical X-Y plotter 26. Battery 10 is connected inseries with power output circuit 18 and is adapted to be supplied withenergy therefrom. As will be explained, power output circuit 18 isselectively controlled such that this energy may be considered to be acharging current during one mode of operation and a charging voltageduring another mode of operation. In order to supply the requisite highcurrent levels to battery 10, power output circuit 18 is coupled to anAC power supply line 19, such as 110/220 volt 60 Hz mains. Oneembodiment of power output circuit 18 is described in greater detailhereinbelow with respect to FIG. 4. It will be appreciated that, undersuitable control, the power output circuit converts the AC powersupplied thereto from AC line 19 to a controlled DC current or DCvoltage which, in turn, is supplied to charge battery 10.

A shunt element 20, such as a high-current, low-resistance resistor, isconnected in series between battery 10 and power output circuit 18. Thepurpose of shunt element 20 is to produce a voltage thereacross which isdirectly related to the DC current supplied to the battery. This voltagerepresentation of the battery current is referred to herein merely as ameasure of the battery current and is utilized in a manner describedmore fully below.

Power output circuit 18 is controlled by a current control signal or bya voltage control signal selectively supplied thereto via switch 16.This switch is utilized as a test/charge switch and is depicted as anelectro-mechanical switch having a movable element selectively engagedwith either a test contact T or a charge contact C. Test contact T iscoupled to the output of variable current source 12, and charge contactC is coupled to the output of voltage source 14.

Variable current source 12 is adapted to generate a current controlsignal which gradually varies with respect to time. In one embodiment,variable current source 12 serves to generate a triangular currentcontrol signal having a gradually increasing portion followed by agradually decreasing portion. This current control signal, when suppliedto power output circuit 18, controls the latter to supply acorresponding charging current to battery 10. Preferably, variablecurrent source 12 functions to generate a trapezoidal-shaped currentcontrol signal having a gradually increasing portion, followed by asubstantially constant current level portion, followed by a graduallydecreasing portion, as illustrated in FIG. 1. The increasing, orpositive ramp, portion of the current control signal preferablyincreases linearly with respect to time so as to produce a chargingcurrent which likewise increases linearly from an initial zero level toa maximum current level. This maximum current level is set as a functionof the actual charge capacity of battery 10, for example, the maximumcurrent level is equal to the charge capacity of the battery divided bythe factor 2.5. The decreasing, or negative ramp, portion of the currentcontrol signal preferably varies linearly with respect to time so as toproduce a corresponding charging current whose slope is equal to butopposite that of the positive ramp portion. For example, if battery 10has a capacity of 800 AH, the maximum charging current is on the orderof about 320 amps, and the slope of the positive and negative rampportions thereof is on the order of about 1000 amps/sec. Preferably,this slope remains constant regardless of the maximum current levelwhich is attained by the charging current, that is, this slope remainsconstant regardless of the actual capacity of battery 10. Of course,other slopes may be selected, as desired.

Preferably, switch 16 remains engaged with its test contact T for apredetermined duration, referred to herein as the test cycle. Duringthis test cycle, variable current source 12 supplies the aforedescribedcurrent control signal to power output circuit 18, resulting in a "test"charge current supplied to battery 10 during this test cycle. It isappreciated that, if the duration of the test cycle is fixed, and if theslopes of the positive and negative ramp portions of the current controlsignal likewise are fixed, then the time interval during which theconstant current level is supplied to battery 10 is a function of themaximum charging current level attained during the positive ramp portionof the control current signal. That is, since the charging current willreach a lower maximum current level in a shorter period of time, thetime duration of the constant current level is relatively greater.Alternatively, the duration of the constant current level may remainfixed such that the overall time duration of the test cycle is variable.In this alternative embodiment, the test cycle duration is shorter ifthe maximum current level to which the charging current may rise isless. For example, if it is established that the test cycle durationremains fixed at 8 seconds, and if the maximum charging current level isset at 300 amps, then the positive ramp portion of the current controlsignal extends for about 3 seconds, followed by a constant currentcontrol signal level that extends for about 2 seconds, followed by thenegative ramp portion of the current control signal which extends forabout 3 seconds. For this same 8 second test cycle duration, if themaximum charging current level is set at 350 amps, then the positiveramp portion extends for about 3.5 seconds, followed by the constantcurrent level portion which extends for about 1.0 seconds, followed bythe negative ramp portion which extends for about 3.5 seconds. In thealternative embodiment, if the constant charging current level is toextend for about 2 seconds, then, for a maximum charging current levelof 300 amps, the positive ramp portion extends for about 3 seconds,follow by the 2 second constant current level portion, followed by thenegative ramp portion which extends for about 3 seconds, resulting in anoverall test cycle of about 8 seconds. However, if the maximum chargingcurrent level is established to be about 350 amps, then it isappreciated that the overall test cycle duration extends for about 9seconds.

As will be decribed below, during the test cycle duration, variousconditions and characteristics of battery 10 are measured anddetermined. Following the test cycle, switch 16 is changed over so as toengage its charge contact C. Then, a charge cycle is carried out. Duringthis charge cycle, power output circuit 18 is controlled by voltagesource 14 to supply battery 10 with a controllable charging voltage.

Voltage source 14 is adapted to generate a voltage control signal whichis substantially ramp-shaped. The voltage source is provided withmanually operable adjustments, such as adjustment knobs 15 and 17,adapted to adjust, or change, the slope and initial voltage level V_(o),respectively, of the ramp-shaped voltage control signal. Advantageously,the slope of this voltage ramp is adjustable so as to be related to thestate-of-charge of battery 10. More particularly, during the test cycle,the battery voltage which is produced in response to the test chargingcurrent supplied thereto generally will be dependent upon thestate-of-charge of the battery, and the slope of the voltage rampgenerated by voltage source 14 is related to this voltage. It may beappreciated that, if the state-of-charge of battery 10 increases, thebattery voltage produced in response to the test charging currentsupplied thereto likewise will increase. Preferably, as this batteryvoltage reaches certain predetermined levels, the slope of the voltageramp generated by voltage source 14 will vary. Preferably, slopeadjustment knob 15 is provided such that an operator may reduce theslope of the voltage ramp when the battery voltage, which is measuredduring each test cycle, exceeds predetermined levels. As a numericalexample, if battery 10 exhibits a relatively low initialstate-of-charge, then slope adjustment knob 15 may be set such that thevoltage ramp generated by voltage source 14 results in a correspondingramp-shaped charging voltage having a slope equal to 0.0023volts/min./cell. When, during a succeeding test cycle, the batteryvoltage increases, as a result of preceding charging cycles, so as toreach a level of 2.25 volts/cell during a test cycle, the slope of theramp-shaped charging voltage supplied to battery 10 is reduced to 0.0019volts/min./cell. This reduction may be attained by appropriately settingslope adjustment knob 15. Subsequently, during a test cycle, if thebattery voltage is measure to be about 2.35 volts/cell, the slope of theramp-shaped charging voltage is reduced further to, for example, 0.0015volts/min./cell. Further reductions in the slope of the charging voltagemay be made, as desired, when the battery voltage, during succeedingtest cycles, exceeds other threshold levels.

Although not shown herein, suitable "start" switches may be provided soas to actuate variable current source 12 when switch 16 is changed overto engage its test contact T, and to actuate voltage source 14 when theswitch is changed over to engage its charge contact C. Switch 16 may bemanually changed over from one contact to another or, alternatively, atimer may be provided to effect this change over. As mentioned above,each test cycle may be fixed for a duration of about 8 seconds or,alternatively, the test cycle may be variable with a maximum duration onthe order of about 10 seconds. Each charge cycle may be fixed and mayexhibit a duration on the order of about 10 to 20 minutes.

The operation of the apparatus illustrated in FIG. 1 now will bedescribed. When a test cycle is initiated, as when switch 16 engages itstest contact T, variable current source 12 supplies the aforedescribedvarying current control signal to power output circuit 18, whereby thepower output circuit supplies a corresponding controllably varying testcharging current to battery 10. For convenience, the current supplied bypower output circuit 18 to the battery during the test cycle is referredto herein as the test current. As discussed previously, it is preferredthat this test current be substantially trapezoidal shaped, although atriangular shaped test current may be supplied. As alternativemodifications, the test current may be sinusoidally shaped, and stillother wave shapes may be utilized. Regardless of the particular shape ofthe test current, it is important merely that the test current increasewith respect to time and then decrease with respect to time.

As the test current is supplied to battery 10, a corresponding voltageis produced across shunt element 20. This voltage, which is a directrepresentation of the magnitude of the test current supplied to battery10, is applied to input terminals 24 of X-Y plotter 26. This plotter maybe a conventional two-coordinate ink plotter whose abscissa is suppliedwith a voltage measurement representing the test current through battery10. X-Y plotter 26 includes another input terminal 22 coupled acrossbattery 10 and adapted to receive the actual battery output voltagewhich is produced in response to the test current supplied thereto. Ifthe current measurement supplied to input terminals 24 of plotter 26 isused to determine the abscissa of each two-coordinate graphical plot,then the voltage measurement supplied to input terminal 22 of theplotter is adapted to control the ordinate of that plot. Thus, plotter26 generates a graphical characteristic whose X-axis is a function ofbattery test current and whose Y-axis is a function of battery voltage.The resultant X-Y plot is a voltage-current (V-I) characteristic ofbattery 10 during a test cycle. This V-I characteristic is illustratedin FIG. 1 as curve A.

Circuitry may be coupled to X-Y plotter 26 to obtain the derivative, ortime-differential, of V-I characteristic A. This derivativecharacteristic is graphically drawn by the X-Y plotter. In FIG. 1, curveB represents the time-derivative of V-I characteristic A.

Before describing the operation of the apparatus shown in FIG. 1 duringa charge cycle, further description is provided with respect to the V-Icharacteristics which are obtained during various test cycles of battery10. Referring now to FIG. 2A, let it be assumed that battery 10 exhibitsa relatively low initial state-of-charge. Accordingly, when the testcurrent described above is supplied to the battery during an initialtest cycle, for example, when a triangular-shaped or trapezoidal-shapedtest current is supplied, the resultant voltage-current characteristicthat is obtained while that test current is supplied is illustrated bycurve A shown in FIG. 2A. If the capacity of the battery is not known,and if the number of cells included in that battery also is not known,then the maximum current level, or "peak" of the test current suppliedto battery 10, may be established initially at a relatively low level sothat the voltage produced across battery 10 in response thereto remainsbelow the gas voltage level V_(gas), such as a test current peak levelon the order of about 200 amps. It is seen that the voltage-currentcharacteristic A₁ which is obtained during the positive ramp portion ofthe test current is not identical to the voltage-current characteristicA₂ which is obtained during the negative ramp portion of the testcurrent. That is, the voltage-current characteristic exhibitshysteresis. One possible explanation of this hysteresis may be that,even though the test current is supplied for only a relatively brieftime interval, this test current may be sufficient to alter theelectro-chemical characteristics of the battery, thereby modifying thedynamic voltage-current characteristic thereof. FIG. 2A also illustratesthe derivative of voltage-current characteristic A, this derivativecurve being illustrated as curve B. More particularly, derivative curveB₁ corresponds to the derivative of voltage-current characteristic A₁,obtained during the positive ramp portion of the test current; andderivative curve B₂ corresponds to voltage-current characteristic A₂which is obtained during the negative ramp portion of the test current.

The slope of the dynamic voltage-current characteristic A is a functionof the actual charge capacity of battery 10. For a particular battery,although the state-of-charge thereof may vary, such as when the batteryis charged, thereby changing the dynamic voltage-current characteristicthereof, the slope of that dynamic voltage-current characteristicnevertheless remains substantially constant. However, if the actualcharge capacity of that same battery changes, such as if the battery hadnot been charged to its proper level during many charging operations, ordue to a change in the electro-chemical characteristic thereof, theslope of the dynamic voltage-current characteristic will change. Theslope of the dynamic voltage-current characteristic is inversely relatedto the charge capacity of the battery. Hence, for batteries havinghigher charge capacities, the slopes of the dynamic voltage-currentcharacteristics obtained for such batteries are relatively lower. Thatis, for such batteries, V-I characteristic curve A will be less steep.Charts, or plots, of typical voltage-current characteristic curves forbatteries having different charge capacities may be prepared, and theactual dynamic voltage-current characteristic which is obtained for abattery under test then may be compared to one of these plots in orderto determine the actual capacity of that battery. Alternatively, atable, such as a "look-up" table, which correlates different batterycharge capacities and V-I slopes may be prepared and utilized todetermine the particular charge capacity of the battery under test.

From FIG. 2A, it is seen that the open-circuit voltage of battery 10,that is, the voltage which is produced in response to a test current ofzero amps, is equal to V_(o). From observation, it has been found thatthe number of cells N included in the battery under test may beapproximated by dividing the initial open-circuit voltage by the factor2. Thus, N=V_(o) /2. Typical open-circuit voltages for conventionallead-acid batteries range between 1.8 volts/cell to 2.2 volts/cell.Hence, for a conventional 6-cell lead-acid battery, the initialopen-circuit voltage V_(o) may be expected to be within the range of10.8 volts to 13.2 volts.

Various battery conditions may be determined from the dynamicvoltage-current characteristic which is obtained during a test cycle ofbattery 10. For example, for a battery having a predetermined number Nof cells, the initial open-circuit voltage V_(o) may be expected to bewithin a particular range. If the actual open-circuit voltage is belowthat range, it may be concluded that the battery is drasticallyunder-charged, or that a fault condition is present. That is, thebattery may be defective. Also, for a battery having N cells and aparticular initial open-circuit voltage V_(o), the actual chargecapacity thereof may be expected to be within a predetermined range.However, if the slope of the dynamic voltage-current characteristicwhich is obtained is too high or too low, it may be concluded that theactual charge capacity, which is related to that slope, falls withoutthe predetermined range, thereby indicating the possibility of a defect.

As yet another example of battery conditions which can be determined, ifa relatively low initial open-circuit voltage V_(o) is measured, thusrepresenting a relatively low initial state-of-charge, the dynamicvoltage-current characteristic A should be substantially free of abruptchanges, or discontinuities. Although such discontinuities are expectedas the state-of-charge of the battery increases, as will be described,the presence of such discontinuities in the V-I characteristic at lowstates-of-charge may be indicative of a defect. For example, one or morecells of the battery may contain broken plates or low levels ofelectrolyte. These defective conditions are indicated by a disturbancein the V-I characteristic at voltage levels less than a predeterminedthreshold, for example, at voltage levels less than the gas voltagelevel V_(gas). For most lead-acid batteries, the gas voltage levelV_(gas) is equal to 2.35 volts/cell.

Yet another indication of a possibly defective condition of battery 10is the amount of hysteresis that is present in the dynamicvoltage-current characteristic A. For most lead-acid batteries having Ncells, it is expected that a significant amount of hysteresis will bepresent. Examples of such hysteresis may be obtained by plotting"reference" dynamic voltage-current characteristics obtained for variousdifferent batteries. If the actual hysteresis of the dynamicvoltage-current characteristic obtained from a battery under test is farless than the expected hysteresis thereof, it is possible that thetested battery may be defective. This may be determined by comparing theactual voltage-current characteristic to such reference characteristics.Alternatively, insufficient hysteresis, indicative of a defectivecondition, may be determined if the open-circuit voltage which isproduced when the test current returns to zero is equal to or almostequal to the open-circuit voltage which is produced when the testcurrent initially is zero.

If the battery under test is subjected to a charging operation, as willbe described, or if the initial state-of-charge thereof is higher thanthat which has been described for the battery which yields the V-Icharacteristic shown in FIG. 2A, the dynamic voltage-currentcharacteristic which is obtained may appear as shown in FIG. 2B. Acomparison of the V-I characteristics of FIGS. 2A and 2B indicates that,in the battery which exhibits a higher state-of-charge (whose V-Icharacteristic is shown in FIG. 2B), the initial open-circuit voltageV_(o) is higher. Also, the hysteresis between V-I characteristic A₁,obtained during the positive ramp portion of the test current, and V-Icharacteristic A₂, obtained during the negative ramp portion of the testcurrent, has increased. Still further, curves A₁ and A₂ no longerexhibit substantially constant slope. Rather, the slope of curve A₁ isseen to increase when a first test current level is reached, and thenthis slope decreases abruptly when a second, higher test current levelis reached. During the negative ramp portion of the test current, it isseen that the slope of curve A₂ increases abruptly when the test currentis reduced from its maximum level and then, subsequently, the slopegradually decreases. The derivative B of this dynamic voltage-currentcharacteristic A clearly shows the abrupt changes in the slopes ofcurves A₁ and A₂. In particular, derivative curve B₁ illustrates anabrupt reduction in the slope of curve A₁ ; and derivative curve B₂illustrates an abrupt increase in the slope of curve A₂. These abruptchanges, or discontinuities, in the slope of the dynamic voltage-currentcharacteristic A occur at relatively higher test current levels.

FIG. 2B also illustrates that the battery voltage which is produced inresponse to the test current supplied thereto exceeds the gas voltagelevel V_(gas) when the test current reaches a corresponding thresholdlevel. It is expected that the gas voltage level V_(gas) will beexceeded in response to the test current if the state-of-charge of thebattery is greater than a predetermined amount, this predeterminedcharge level being represented by the open-circuit battery voltageV_(o). If, however, the battery voltage does not exceed the gas voltagelevel V_(gas) for this state-of-charge, it may be interpreted that thebattery under test is defective. Also, for this state-of-charge, if thebattery voltage which is produced in response to the maximum testcurrent supplied thereto greatly exceeds the gas voltage level V_(gas),or is approximately equal to a maximum voltage level V_(max), a faultcondition may be present. Hence, the battery condition may be determinedby observing the dynamic voltage-current characteristic which isobtained and by comparing the resultant V-I characteristic withreference characteristics. Such reference characteristics may beprepared, in advance, by testing known, "good" batteries at differentstates-of-charge.

Although the charge condition (i.e. state-of-charge) of battery 10 mayhave increased, as represented by the plot shown in FIG. 2B relative tothe plot shown in FIG. 2A, the "mean" slope of the dynamicvoltage-current characteristic shown in FIG. 2B remains approximatelyequal to that shown in FIG. 2A. This means that the actual chargecapacity of the battery has not varied. It may be appreciated that, ifthe slope of the dynamic voltage-current characteristic changessignificantly, for example, if the slope changes as the battery ischarged, such a significant change in slope may be representative of apossibly faulty, or defective, condition.

FIGS. 2C and 2D are dynamic voltage-current characteristics which areobtained either for the same battery whose state-of-charge hasincreased, as by subjecting that battery to charging operations, to bedescribed, or such figures may represent the voltage-currentcharacteristics which are obtained for batteries having different,higher initial states-of-charge. From FIG. 2C, it is seen that thegeneral shape of the dynamic voltage-current characteristic A is similarto the general shape of the dynamic voltage-current characteristic shownin FIG. 2B. In FIG. 2C, the amount of hysteresis exhibited by the V-Icharacteristic is greater. Also, the open-circuit voltage V_(o) in FIG.2C is greater than that shown in FIG. 2B. Hence, the state-of-charge ofthe battery whose V-I characteristic is represented in FIG. 2C isgreater than the state-of-charge of the battery whose V-I characteristicis illustrated in FIG. 2B. Also, in FIG. 2C, the slope of curve A₁,obtained in response to the positive ramp portion of the test current,is seen to gradually increase and then, at a test current level which isless than the test current level of FIG. 2B, abruptly decreases.Similarly, the slope of curve A₂ in FIG. 2C is seen to abruptly increaseat a test current level which is lower than the test current level whichproduces the abrupt increase in slope in FIG. 2B. Derivative curve B inFIG. 2C illustrates the locations (i.e. test current levels) at whichsuch abrupt changes in slope occur. A comparison of FIGS. 2B and 2Cindicates that, as the charge level of the battery increases, theaforementioned abrupt changes in slope of the dynamic voltage-currentcharacteristic occur in response to lower test current levels.

FIG. 2C also illustrates that the battery voltage quickly exceeds thegas voltage level V_(gas) in response to the triangular or trapezoidaltest current supplied to battery 10. The maximum voltage produced inresponse to this test current now asymptotically approaches the maximumvoltage V_(max). From FIG. 2B, it is seen that, when battery 10 exhibitsa lower charge level (or state-of-charge), the maximum battery voltagewhich is produced in response to the test current is substantially lessthan the maximum voltage level V_(max). For most lead-acid batteries,the maximum voltage which can be produced in response to theaforedescribed test current is on the order of about 2.58 volts/cell.For example, for a 6-cell lead-acid battery, the maximum battery voltagewhich is produced in response to the test current is equal to about 15.5volts. If the dynamic voltage-current characteristic which is obtainedfrom a battery under test exceeds this maximum voltage level, thebattery possibly may be defective.

The "mean" slope of the V-I characteristic A shown in FIG. 2C isapproximately equal to the "mean" slope of the V-I characteristics shownin FIGS. 2A and 2B. This indicates that the actual charge capacity ofthe battery remains the same, even though the state-of-charge thereofhas increased. If the "mean" slope varies substantially, this may beindicative of a possibly faulty condition in battery 10.

In FIG. 2D, the dynamic voltage-current characteristic for asubstantially fully-charged battery is illustrated. The derivative curveB also is illustrated. It is seen from this derivative curve that,during the positive ramp portion of the test current, an abrupt decreasein slope of the dynamic voltage-current characteristic occurs at a muchlower test current level than occurs for batteries of lesser charge.Likewise, derivative curve B illustrates an abrupt increase in the slopeof the dynamic voltage-current characteristic during the negative rampportion of the test current, which abrupt increase occurs at a lowertest current level. FIG. 2D also indicates that the open-circuit batteryvoltage V_(o) exceeds the gas voltage level V_(gas) ; and the maximumvoltage produced by the battery in response to the test currentasymptotically approaches the maximum threshold level V_(max) inresponse to lower test current levels. Still further, the hysteresisbetweeen curves A₁ and A₂ is greater for the battery which is more fullycharged. Stated otherwise, the dynamic voltage-current characteristic ofFIG. 2D appears "fatter" than the dynamic V-I characteristic curvesshown in FIGS. 2A-2C.

From the derivative curves B shown in FIGS. 2A-2D, it may be seen that,as the state-of-charge of the battery increases, the aforementionedabrupt changes, or discontinuities, in the slopes of the dynamicvoltage-current characteristics occur at lower test current levels. Thatis, such discontinuities occur in the derivative curve B closer to theordinate. This may be turned to account to indicate when battery 10 hasbeen charged to its proper, fully-charged level. For example, fromobservation, it may be determined that, when battery 10 is fullycharged, the abrupt discontinuities present in the derivative curve Boccur at predetermined test current levels. If, during a test cycle ofbattery 10, the derivative curve B is obtained having discontinuitieswhich occur at the same predetermined test current levels, it may beconcluded that battery 10 is fully charged.

Returning now to FIG. 1, it now is appreciated that, after an initialtest cycle, various conditions and characteristics of battery 10 may bedetermined. For example, depending upon the slope of the dynamicvoltage-current characteristic which is obtained, the actual chargecapacity of that battery may be determined. Likewise, depending upon theinitial open-circuit voltage V_(o), the state-of-charge of that batterymay be determined. If the dynamic voltage-current characteristic whichis obtained differs substantially from the representativevoltage-current characteristics shown in FIGS. 2A-2D, it may beconcluded that a possible defect or fault is present. If the dynamicvoltage-current characteristic which is obtained undergoes abruptchanges, or discontinuities, at locations where such abrupt changes ordiscontinuities are not expected, for example, at locations well belowthe gassing level, such abrupt changes or discontinuities may beindicative of a fault condition. Likewise, various other characteristicconditions may be determined by comparing the actual dynamicvoltage-current characteristic which is obtained to representative V-Icharacteristics, or "signatures" which are obtained from known batterieshaving certain predetermined faults.

After a test cycle having a predetermined short duration, as describedabove, is carried out, switch 16 is changed over to engage chargecontact C. Now, a charge cycle is carried out. In the charge cycle, theramp control voltage signal is generated and supplied to power outputcircuit 18, whereupon a corresponding ramp-shaped charging voltage isapplied to battery 10. It is important to note that, although acontrolled charging voltage is supplied to the battery, the currentdrawn by that battery in response to this voltage is not controlled.Preferably, the current drawn by the battery is monitored to make surethat it does not exceed a predetermined maximum current level, therebyavoiding a potentially harmful condition and preventing damage to thebattery. As mentioned above, the charge cycle is carried out for a timeinterval on the order of about 10 to 20 minutes. During this chargecycle duration, the slope and initial charge voltage level arecontrolled. The slope is controlled in accordance with the followingtable which is merely exemplary:

                  TABLE I                                                         ______________________________________                                        Slope                    Battery Voltage                                      (volts per minute per cell)                                                                            (volts per cell)                                     ______________________________________                                        0.0023            until  2.25                                                 0.0019            "      2.35                                                 0.0015            "      2.4                                                  0.0010            "      2.6                                                  ______________________________________                                    

It will be appreciated that the charging voltage is terminated if thebattery voltage reaches 2.6 volts per cell. That is, if the batteryvoltage exceeds the maximum threshold level V_(max), the chargingoperation is terminated. This prevents damage to the battery.

The initial voltage of the ramp charging voltage is related to theopen-circuit voltage V_(o) which is measured during an immediatelypreceding test cycle. For example, the ramp charging voltage maycommence at a level which is on the order of about 0.1 to 0.6 voltsgreater than the measured open-circuit voltage V_(o).

Switch 16 is changed over between its test contact T and its chargecontact C periodically so as to carry out repeated, alternate test andcharge cycles. Each test cycle is conducted in the manner describedhereinabove; and during each test cycle, the dynamic voltage-currentcharacteristic of battery 10 is measured. During each charge cycle,which is seen to be carried out over a much greater time duration thaneach test cycle, the ramp voltage commences at a level that is relatedto the previously-measured open-circuit voltage V_(o) obtained from thepreceding test cycle. Also, the slope of the ramp voltage is controlledin accordance with Table I. Thus, as the state-of-charge of battery 10increases, the ramp charging voltage commences at successively higherlevels; and the slope of the ramp voltage decreases as higher batteryvoltages are measured. Desirably, battery 10 is charged quickly to itsgassing level. Hence, the slope of the ramp charging voltage is steeperfor battery voltages which are less than the gas voltage level V_(gas).When the gas voltage level is reached, the slope of the ramp chargingvoltage is reduced; as by operating slope adjustment knob 15, and theslope is further reduced when the predetermined battery voltage levelsset out in Table I are reached.

It will be appreciated that, during each subsequent charge cycle, thecharge level, or state-of-charge of battery 10 increases. Consequently,during each test cycle following a charge cycle, the dynamicvoltage-current characteristic which is obtained will exhibit aprogressively changing shape and attitude, as depicted by the selectedV-I characteristics of FIGS. 2A-2D. Ultimately, the condition of thebattery which is measured during a test cycle will be substantiallyidentical to the condition thereof which had been measured during apreceding test cycle. Stated otherwise, the dynamic voltage-currentcharacteristic which is obtained during a particular test cycle will besubstantially identical to the preceding dynamic voltage-currentcharacteristic. This means that there has been no change in the chargecondition, or state-of-charge of battery 10. Since this no-changecondition will occur substantially only when the battery is fullycharged, it now is determined that battery 10 has been charged to itsproper, full level.

As an example of detecting when battery 10 has been fully charged, thedynamic voltage-current characteristic A shown, for example, in FIG. 2D,will be substantially congruent with a preceding voltage-currentcharacteristic. As another example, the discontinuities in derivativecurve B will occur at substantially the same test current levels asduring a preceding test cycle. Still further, if the test current levelsare measured, or detected, when derivative curve B undergoes theillustrated discontinuities, then, as battery 10 is charged, suchdiscontinuities will occur at lower and lower test current levels. Whensuch test current levels at which these discontinuities occur are notreduced further, then it is determined that battery 10 has been fullycharged. Thus, by comparing the results which are obtained during a testcycle to the results which are obtained during a preceding test cycle,it can be determined when the battery has been fully charged. At thattime, charging of the battery is terminated. That is, no further chargecycles need be carried out. If desired, however, further test cycles maybe conducted so as to continue to monitor the condition of battery 10.

FIGS. 2B-2D illustrate an additional curve C. This curve C representsthe current which flows to battery 10 in response to the ramp chargingvoltage supplied thereto during each charge cycle. As mentioned above,the current supplied to battery 10 during a charge cycle is notcontrolled. That is, the current drawn by the battery is not limited.Hence, battery 10 draws such current as is determined by the chargingvoltage supplied thereto, the internal impedance of the battery and theso-called I² R losses therein. From curves C, it is seen that, as thecharging voltage level increases, the current drawn by battery 10likewise increases. This current-voltage relationship remainssubstantially linear until the charging voltage level reaches the gasvoltage V_(gas). At that time, the effective internal impedance of thebattery increases such that the current now drawn thereby decreases evenas the charging voltage level continues to increase. Curves C representthis decrease in current, even though the charging voltage increases,following the onset of the gassing condition. From FIG. 2D, it isfurther seen that the current drawn by the battery continues to decreaseuntil a substantially constant current is drawn regardless of furtherincreases in the charging voltage level. This condition, wherein thebattery current no longer decreases with voltage, is attained when thebattery is fully charged. Hence, another technique by which it may bedetermined when battery 10 has been fully charged may comprise themonitoring of the battery current drawn during each charge cycle anddetecting when this battery current no longer decreases with an increasein charging voltage. When that point is detected, it may be consideredthat battery 10 has been fully charged.

From the foregoing, it is appreciated that the charge condition ofbattery 10 is determined as a function of the dynamic voltage-currentcharacteristic A which is obtained during each test cycle. Although thegas voltage level V_(gas) is substantially the same for most lead-acidbatteries, a "look-up" table may be provided which correlates chargecapacity and state-of-charge with gas voltage. Since the slope of thedynamic voltage-current characteristic can be measured so as to derivethe actual charge capacity, and since the open circuit voltage V_(o) canbe measured so as to derive an approximation of the state-of-charge ofthe battery, the gas voltage level V_(gas) may be determined for theparticular battery then being tested. If discontinuities in the slope ofthe voltage-current characteristic, such as the discontinuitiesillustrated for derivative curves B, are detected before the batteryvoltage reaches the gas voltage level V_(gas), it may be considered thatthe battery under test is defective. Likewise, if such discontinuitiesare not sensed even after the battery voltage exceeds the gas voltagelevel, it may be considered that an improper or unusual condition ispresent. Such conditions may be displayed by automatic sensing anddisplay apparatus, described in greater detail hereinbelow.

As an alternative to the aforementioned "look-up" table which correlatesthe gas voltage levels, charge capacities and states-of-charge fordifferent batteries, the gas voltage level of the battery being testedmay be determined by sensing the aforementioned discontinuities in thevoltage-current characteristic. It may be assumed that, if thestate-of-charge of the battery, as derived from the open-circuit voltageV_(o), exceeds a predetermined charge-level threshold, then suchdiscontinuities in the voltage-current characteristic will occur whenthe gas level of the battery is exceeded. However, if suchdiscontinuities are detected when the charge-level of the battery isless than the aforementioned predetermined level, then it may beconsidered that a fault condition is present. Hence, the occurrence ofsuch discontinuities may be used to determine when the battery has beencharged to its gassing condition. In addition, and as has been describedabove, if the current drawn by the battery during each charge cyclethereof is monitored, the gassing condition may be determined by sensingwhen this monitored current begins to decrease. Curves C, as shown inFIGS. 2B-2D, represent this relationship between the ramp chargingvoltage and the battery current for different states-of-charge.

Although not shown in FIG. 1, the current drawn by battery 10 duringeach charge cycle thereof may be monitored. If, during a charge cycle,this monitored current exceeds a predetermined maximum current level,the magnitude of the charging voltage may be reduced. This avoids apotentially dangerous condition which, if not corrected, will result indamage to the battery. The maximum current level which should not besurpassed preferably is a function of the charge capacity of battery 10.As discussed above, the charge capacity of the battery is related to theslope of the dynamic voltage-current characteristic A thereof. As anumerical example, the maximum battery current during the charge cyclemay be derived by dividing this actual charge capacity by the factor3.75. Consequently, for batteries which exhibit relatively higher chargecapacities, the maximum currents which may be drawn during each chargecycle may be substantially higher than the maximum currents which may bedrawn for batteries having lower charge capacities.

In the foregoing discussion, it is preferred that the test currentsupplied to battery 10 by power output circuit 18 in response tovariable current source 12 be either a triangular-shaped test current ora trapezoidal-shaped test current. Advantageously, if atrapezoidal-shaped test current is used, an "equalizing" charge need notbe supplied after the charging operation is completed. This is becausethe relatively high current level of the constant current portion whichfollows the positive ramp and precedes the negative ramp of the testcurrent achieves a function which obviates such an equalizing charge.

When a lead-acid battery is charged, the electrolyte therein may exhibitsome degree of stratification. Such stratified acid tends to reduce thecharge capacity of the battery and, moreover, results in a reduction inthe state-of-charge thereof. To avoid such stratification, it isdesirable to "stir" the acid, as by inducing bubbles therein. Suchstirring, or mixing of the acid makes the characteristics of the batterymore uniform and brings the battery closer to its rated capacity andoutput levels. Although this is one purpose of supplying an equalizingcharge to a battery, conventional battery chargers require a number ofhours for supplying low equalizing charging currents to the battery.However, such low charging currents induce relatively small bubbles inthe acid which may not be strong enough to effect proper mixing of theacid. Contrary to such conventional chargers, the trapezoidal-shapedtest current which is used during the test cycle of the presentinvention supplies a very high substantially constant test current levelto the battery during short time intervals. Such high current levelsinduce large bubbles in the acid, resulting in desirable, enhancedmixing. Since the duration of such high test current levels isrelatively brief, battery damage is avoided.

While such "stirring" may be carried out during each periodic testcycle, in an alternative embodiment, such stirring is carried out onlyduring selected test cycles. Consequently, during those test cycleswherein stirring need not be performed, the test current may betriangular shaped.

The operation carried out by the apparatus illustrated in FIG. 1 hasbeen described as being controlled by an operator. In accordance with apreferred embodiment of this invention, the operation carried out by theapparatus in FIG. 1 may be performed automatically, under the control ofa programmed data processor, by the apparatus illustrated in FIG. 3. InFIG. 3, a programmed data processor referred to as central processingunit (CPU) 30 is connected with a memory 36, such as a read only memory(ROM) in which the program for CPU 30 is stored; and the CPU is furtherconnected with a random access memory (RAM) in which data that isderived from and used in the test and charge cycles are stored. CPU 30also is coupled to a digital-to-analog converter 32 which, in turn, iscoupled to power output circuit 18. The D/A converter functions tosupply the aforedescribed current and voltage control signals to thepower output circuit during test and charge cycles, respectively, suchthat the test current and charge voltages may be supplied to battery 10,as discussed above. CPU 30 also is coupled to an analog-to-digitalconverter 34 which functions to convert the voltage V sensed acrossbattery 10 and the current I through the battery to correspondingdigital values. Such digital representations of battery voltage andcurrent are supplied to CPU 30 wherein they are utilized and processedin conjunction with the test and charge cycles.

The functions performed by switch 16, variable current source 12 andvoltage source 14 of FIG. 1 are carried out in an analogous manner byCPU 30. Thus, the CPU establishes the test and charge cycles alternatelyand repeatedly. During each test cycle, CPU 30 controls D/A converter 32to supply the aforedescribed triangular or trapezoidal-shaped currentcontrol signals to output circuit 18. During each charge cycle, the CPUcontrols the D/A converter to supply the aforedescribed ramp voltagecontrol signal to the power output circuit. In addition, depending uponthe condition of battery 10, as determined during each test cycle, theslope and beginning voltage level of each ramp voltage signal isestablished in a manner analogous to the aforedescribed operation ofadjustment knobs 15 and 17.

Also, CPU 30 processes the voltage and current measurements obtainedduring each test cycle in order to determine the charge capacity,state-of-charge and possible fault or defective conditions of battery10. For example, memory 36 may store digital representations of thevarious voltage-current characteristics for different batteries. CPU 30obtains the dynamic voltage-current characteristic for the battery undertest and compares this characteristic to the stored representations. Inthis manner, various conditions of battery 10 may be determined.Furthermore, mamory 36 may store digital representations of thepreceding voltage-current characteristic which is obtained during apreceding test cycle; and CPU 30 may compare this stored, precedingcharacteristic to the latest voltage-current characteristic thenobtained. In the event of a favorable comparison, for example, if thelatest voltage-current characteristic obtained by CPU 30 issubstantially congruent with the stored, preceding characteristic, theCPU determines that battery 10 has been fully charged, and the chargingoperation is terminated. Alternatively, memory 36 may store the testcurrent levels at which discontinuities in the voltage-currentcharacteristic, obtained during the preceding test cycle, have occurred.CPU 30 then compares the test current levels at which discontinuitiesoccur in the latest voltage-current characteristic to such stored testcurrent levels to determine if there has been any change in suchoccurrences. If no changed is sensed, the CPU determines that thebattery is fully charged.

In a preferred embodiment, memory 36 stores data representations ofvarious "signatures" corresponding to different fault conditions whichmay be present in batteries of different storage capacities, numbers ofcells, states-of-charge, and the like. CPU 30 functions to obtain thedynamic voltage-current characteristic of the battery under test and tocompare this characteristic to such "signatures" to determine if suchfault conditions are present in this battery.

Although not shown, the apparatus of FIG. 3 also may be provided withsuitable displays, such as indicator lamps, which are selectivelyenergized by CPU 30 in the event that particular fault conditions aresensed.

The various "look-up" tables mentioned hereinabove with respect to FIG.1 may be stored in memory 36. Various features, or characteristics, ofthe dynamic voltage-current characteristic which is obtained by CPU 30during a test cycle thus may be compared to the data stored in such"look-up" tables in order to determine, inter alia, the state-of-chargeof battery 10, the charge capacity thereof as a function of the slope ofthe voltage-current characteristic, the expected gas voltage levelV_(gas), the number of cells of battery 10 as a function of the initialopen-circuit voltage V_(o), the expected locations of discontinuities inthe voltage-current characteristic as a function of battery chargecapacity, charge level and number of cells, the maximum battery currentlevels, during test and charge cycles, as a function of charge capacity,and the like.

A general flow chart of the program for CPU 30 is set out in FIG. 5.Before describing this flow chart, which will facilitate anunderstanding of the automatic charging apparatus illustrated in FIG. 3,reference is made to FIG. 4 which is a block diagram of power outputcircuit 18. This power output circuit is comprised of avoltage-controlled rectifier 40, an inverter 42, a transformer 44 and anoutput recitifier 48. Voltage controlled rectifier 40 is adapted to besupplied with AC power, as from AC line 19, and to rectify this AC powerto produce DC currents in response to a control signal supplied thereto.This control signal is produced by CPU 30 and is dependent upon thedetermined number of cells of battery 10, the actual charge capacity ofthis battery and the state-of-charge thereof. Hence, the DC currentsproduced by voltage-controlled rectifier 40 are a function of thecondition of battery 10.

The DC currents produced by voltage-controlled rectifier 40 are suppliedto inverter 42 which functions to invert these DC currents tocorresponding AC signals. Inverter 42 is controlled by CPU 30 to producean AC signal which, when rectified, corresponds either to thetrapezoidal-shaped test current or the ramp-shaped charging voltage. Asan example, inverter 42 may include a pulse width modulator whichgenerates pulse width modulated signals corresponding to thetrapezoidal-shaped test current and ramp-shaped charging voltage whichshould be supplied to battery 10. In one embodiment, a test currentcomparator is supplied with a signal representing the actual currentflowing through battery 10, as derived by shunt element 20, to comparethis current representation to the current control signal, i.e. to ananalog version of the desired test current level then supplied by CPU30. Any difference therebetween is used to control the pulse widthmodulator accordingly. Hence, the pulse width modulator generates pulseswhose width increases and decreases in a manner corresponding to thepositive and negative ramp portions of the trapezoidal-shaped testcurrent. Such width-modulated pulses control switches, such as SCRswitching devices, thereby generating a switched AC output. Suchinverters are known to those of ordinary skill in the art.

Inverter 42 also may include a charge voltage comparator which issupplied with a signal representing the voltage across battery 10, andwith the voltage control signal, i.e. a signal representing the analogversion of the ramp charging voltage determined by CPU 30. Anydifference between the actual battery voltage and the desired rampvoltage is used to control the aforementioned pulse width modulatorwhich, in turn, operates the SCR switching devices to generate acorresponding switched AC signal at the output of the inverter. During atest cycle, the aforementioned charge voltage comparator is inhibited;and during a charging cycle, the aforementioned test current comparatoris inhibited. Hence, the switched AC output of inverter 42 representsthe appropriate test current during test cycles and also represents theappropriate charging voltage during charge cycles.

The switched AC signal generated at the output of inverter 42 issupplied to rectifier 48 via a transformer 44. The rectifier rectifiesthe switched AC signal, resulting in the appropriate trapezoidal-shapedtest current or ramp-shaped charging voltage during test and chargecycles, respectively. It is appreciated that the magnitude of theswitched AC output from inverter 42 varies as a function of the currentand voltage control signals generated by CPU 30. As the magnitude of theswitched AC output increases, the corresponding rectified DC currentsand voltages correspondingly increase.

Desirably, primary winding 44a of transformer 44 is connected inparallel with a capacitor 46. The purpose of this capacitor is tominimize any change on the overall resonant frequency of transformer 44in the event that the battery is disconnected. That is, if the batteryis disconnected, transformer 44 exhibits a very high inductance which,in the absence of a load, tends to reduce the resonant frequencysignificantly. However, by connecting capacitor 46 in parallel with theprimary winding 44a, the resonant frequency is determined by thecombination of capacitor 46 and the inductance of transformer 44.Consequently, even if the battery is disconnected, there will be littlechange in the resonant frequency of the illustrated circuit.

Resonant frequency is important because inverter 42 operates at veryhigh frequencies, on the order of 20 KHz. By operating at such highfrequencies, sufficient current may be supplied to the battery duringtest and charge cycles without requiring very large transformerstructures. Consequently, the overall weight and size of the chargerapparatus may be reduced substantially.

In accordance with the relatively high switching frequencies of inverter42, it is preferred that rectifier 48 be provided with, for example,three pairs of diodes, each pair being connected to a respectivesecondary winding (only one 44b being shown) of transformer 44. Thecathodes of all of the diodes are connected in common to one terminal ofbattery 10, and the secondary windings are provided with center taps allconnected in common to the other terminal of the battery. Thisembodiment improves the heat distribution in rectifier 48 and, moreover,each of the diodes may exhibit a relatively lower power rating than ifonly two diodes were provided in the rectifier. Since each diode issupplied with smaller AC currents, the diodes may exhibit fasterturn-off times so as to be used at the higher switching frequencies ofinverter 42.

Turning now to FIG. 5, there is illustrated a flow chart of a generalprogram for controlling CPU 30 to carry out alternate and repeated testand charge cycles. The CPU is initialized to a predetermined, initialcondition. In this initialized state, a diagnostic subroutine may becarried out to determine that the CPU is in operable condition, and alsoto determine that battery 10 is properly connected, and that initialdata is stored in appropriate locations of memory 36, and that D/Aconverter 32 and A/D converter 34 are in operable condition. After theinitalized state is established, CPU 30 advances to carry out an initialtest cycle. The subroutine by which the test cycle is carried out isdescribed in greater detail hereinbelow with respect to the flow chartshown in FIGS. 7A and 7B. Suffice it to say that, during the test cycle,the CPU generates successive samples which represent a digitized versionof a trapezoidal current control signal, which control signal isconverted to an analog control signal and supplied to power outputcircuit 18. Hence, in response to this control signal derived from CPU30, the aforedescribed trapezoidal test current is supplied to battery10.

It is appreciated that, as the test current level gradually increases,the voltage across battery 10 correspondingly increases. Since thecharge capacity and state-of-charge of battery 10 has not yet beendetermined, the test current is controlled to make sure that the voltageproduced across the battery in response to this test current does notexceed an initial predetermined voltage level. During this initial testcycle, the predetermined maximum voltage level is set at the gas voltagelevel V_(gas) which, as discussed above, is approximately 2.35volts/cell for a typical lead-acid battery. Unless the operator commandsotherwise, it is assumed that battery 10 is a 6-cell battery.

At the beginning of the test cycle, that is, when the test current issubstantially equal to zero, the voltage across battery 10 is read. Thisvoltage is supplied as an analog signal to A/D converter 34 which, inturn, converts this analog level to a corresponding digitalrepresentation. This digitized voltage signal is supplied to CPU 30whereat it is read. The program of the CPU then advances to divide thisbattery voltage by the factor 2 to approximate the number of cellsincluded in battery 10. As discussed hereinabove, it is expected thatthe initial open-circuit voltage across battery 10, that is, the voltageproduced in response to a substantially zero test current, will be inthe range of about 1.8 volts/cell to about 2.2 volts/cell. Hence, bydividing the total battery voltage by the factor 2, the approximatenumber of cells included in the battery may be ascertained.

After the open-circuit battery voltage V_(o) is determined, CPU 30controls D/A converter 32 to generate the aforedescribed trapezoidaltest current signal. As will be discussed hereinbelow, the CPU may, inaccordance with its program, generate a digital representation of thetest current level, which digital representation is incremented by apredetermined amount in successive time increments, thereby resulting inthe positive ramp portion of the test current control signal. When thistest current reaches a predetermined maximum current level, or when thevoltage produced across battery 10 in response to this test currentreaches its maximum voltage level (assumed, during the initial testcycle, to be equal to V_(gas)), the test current is maintained constantfor a predetermined time, and then this test current is decremented insuccessive time steps so as to produce the negative ramp portion of thetest current control signal. As the test current through battery 10varies in this manner, the voltage across the battery is sensed by A/Dconverter 34 which, in turn, supplies CPU 30 with digitizedrepresentations, or samples of such voltage in successive timeincrements. Hence, CPU 30 now is provided with data representing thetest current supplied to battery 10 and the voltage produced thereacrossin response to that test current. This data is sufficient for CPU 30 toderive the voltage-current characteristic of the battery.

As the sensed battery voltage changes in response to each predeterminedincremental change in the test current, the slope of the voltage-currentcharacteristic is determined. CPU 30 may be programmed to store datarepresenting the instantaneous slope of the V-I characteristic A₁produced in response to the positive ramp portion of the test current,and also to store data representing the instantaneous slope of the V-Icharacteristic A₂ produced in response to the negative ramp portion ofthe test current. These instantaneous slopes then may be averaged, andthe "mean" slope derived therefrom. It is recalled that the mean slopeof the dynamic voltage-current characteristic is related to the actualcharge capacity of battery 10. Memory 36 may store data representativeof this charge capacity as a function of slopes of the V-Icharacteristics and also of the number of cells of different batteries.Based upon such stored data, which may be in the form of typical"look-up" tables, the appropriate charge capacity of battery 10 isdetermined.

Once this charge capacity is determined, CPU 30 advances to establish amaximum test current I_(max) by dividing this determined charge capacityby the factor 2.5. This maximum test current level is stored in anappropriate location of memory 36.

The program of CPU 30 then advances so as to determine the actualstate-of-charge of battery 10 as a function of the determined chargecapacity and initial open-circuit battery voltage. Data representingtypical charge levels may be stored in memory 36 as a function of chargecapacity and open-circuit battery voltage. Hence, this data may beretrieved once the charge capacity and open-circuit voltage are known.Also, based upon this charge level, the gas voltage level V_(gas) may bedetermined. As discussed above, the gas voltage level for most lead-acidbatteries is equal to 2.35 volts/cell. However, the present invention isreadily adapted to be used with those batteries having a gas voltagelevel which is a function of the state-of-charge and charge capacitythereof. Since the state-of-charge and charge capacity of the batteryare known from the previous step of the illustrated program, the gasvoltage level V_(gas) may be readily retrieved from memory 36.

CPU 30 then advances to compare the instantaneous voltage V acrossbattery 10 to the gas voltage level V_(gas) which has been derived inthe manner discussed above. Inquiry is made as to whether theinstantaneous battery voltage is equal to this gas voltage level. Ifnot, inquiry is made as to whether a discontinuity is present in theslope of the determined voltage-current characteristic. If the answer tothis latter inquiry is in the affirmative, an indication that battery 10contains a defective cell is provided. Thus, and as discussed above, ifa discontinuity in the slope of the V-I characteristic is detectedbefore the battery voltage reaches the gas voltage level V_(gas), thisis indicative of a defective cell.

However, if the instantaneous voltage produced across battery 10 isequal to the gas voltage level V_(gas), or if the battery voltage isless than this gas voltage but no discontinuity in the slope of the V-Icharacteristic has been detected, the routine of CPU 30 advances to thenext step illustrated in FIG. 5. This next step serves to determine thecondition of the battery as a function of the dynamic voltage-currentcharacteristic which has been obtained, as a function of the chargecapacity which has been determined in a previous step, and as a functionof the charge level which also has been determined in a previous step.For example, memory 36 may be provided with a suitable look-up table inwhich data representing different battery conditions, such as defectiveconditions, is correlated with charge capacity, charge level, senseddiscontinuities in the V-I characteristic, and the like. Since all ofthis information either has been determined in previous steps, or isbeing read from A/D converter 34, the condition of battery 10 may bereadily determined. As another example, memory 36 may store theaforementioned "signatures" which characterize certain predeterminedfault conditions in batteries of different charge capacity, number ofcells, and the like. The presently obtained battery voltage and current,which may be read directly under the control of CPU 30, may be comparedto such "signatures". In the event of a positive comparisontherebetween, a corresponding fault condition is detected. After sensingthe battery condition, including the aforementioned fault conditions,the illustrated routine of CPU 30 advances so as to display suchdetected fault conditions. As mentioned previously, the battery chargingapparatus may be provided with appropriate display lamps which aresuitably energized to provide an operator with a visual indication ofsuch fault conditions. If desired, any appropriate display may beprovided, such as LED's, LCD's, audible alarms, and the like.

Preferably, but not necessarily, the condition of battery 10 may bedetermined, and detected fault conditions may be displayed, followingthe completion of a test cycle. Thereafter, the charge cycle isexecuted. CPU 30 establishes the beginning, or commencing, voltage levelof the ramp charging voltage as a function of the detectedstate-of-charge of battery 10. It is recalled that the open-circuitbattery voltage which is obtained at the beginning of the test cycle,that is, when the test current is equal to zero, is related to thestate-of-charge of the battery. In a previous step, this state-of-chargehas been determined. Memory 36 also may store ramp voltage levels as afunction of the determined state-of-charge, thereby facilitating a readydetermination of the commencing voltage level for the ramp chargingvoltage. That is, based upon this determined state-of-charge, CPU 30retrieves the corresponding ramp voltage level.

Furthermore, CPU 30 selects the appropriate slope of the ramp chargingvoltage as a function of the battery voltage which was obtained duringthe preceding test cycle. This ramp slope is set out in Table I, above,and is also illustrated in the block identified as "charge cycle" inFIG. 5. It is appreciated that memory 36 may store data corresponding toTable I; and the ramp slope data therein may be retrieved as a functionof the sensed battery voltage during the preceding test cycle. Thus, thelevel and slope of the ramp charge voltage are determined as a functionof the tested condition of battery 10. Stated otherwise, the parametersof the ramp charging voltage are established as a function of thelast-obtained dynamic voltage-current characteristic of battery 10.

After the parameters of the ramp charging voltage have been established,as aforesaid, the program for CPU 30 advances to the routine wherein thecurrent drawn by the battery during the charge cycle is monitored. Asmentioned above, although the battery current is not controlled duringthe charging cycle, it is monitored to make sure that it does not exceeda level which possibly could damage the battery. This maximum currentlevel varies from one battery to another and is a function of the chargecapacity thereof. As a numerical example, the maximum battery currentI_(max) during the charging cycle is maintained less than the chargecapacity (in amp-hours) divided by the factor 3.75. Since the chargecapacity has been determined in a previous step, i.e., as a function ofthe "mean" slope of the voltage-current characteristic, it isappreciated that the maximum current level may be readily determined.Memory 36 may store data representing maximum current levelscorresponding to batteries of different amp-hour charge capacities. CPU30 selects the appropriate maximum current level as a function of thedetermined charge capacity of battery 10. Once this maximum currentlevel is selected, the actual current drawn by battery 10 during thecharging cycle is monitored to make sure that it remains below thismaximum level. In the event that the battery current during the chargingcycle rises to this maximum current level I_(max), the magnitude of theramp charging voltage is reduced so as to correspondingly reduce thebattery current. It is appreciated that this prevents a potentiallyhazardous condition from occurring, and avoids damage to the battery.

After the conclusion of the charging cycle, another test cycle iscarried out. This test cycle is substantially similar to theaforedescribed initial test cycle, except that the magnitude of the testcurrent now may be increased to a level corresponding to the chargecapacity of the battery being tested. Also, in the present test cycle,as well as subsequent test cycles of battery 10, the maximum batteryvoltage which may be produced thereacross now is permitted to be equalto the level V_(max) which is greater than the gas voltage levelV_(gas). It is recalled that, during the initial test cycle, informationregarding the condition of the battery had not yet been obtained. Thus,prior to executing the initial test cycle, the number of battery cells,actual charge capacity, state-of-charge and possible fault or defectiveconditions generally were not known. Consequently, to avoid damage tothe battery, the maximum test current level and maximum battery voltagelevel deliberately were maintained relatively low. Now, however, afterthe initial test cycle has been completed, the aforementioned conditionsand characteristics of the battery are determined. Consequently, themaximum current and voltage levels during this and subsequent testcycles now may be selected as a function of such conditions. Forexample, the maximum current level now may be set to be equal to thecharge capacity of the battery (which has been determined in a previousstep) divided by the factor 2.5. Likewise, in the absence of a faultcondition which would prevent otherwise, the maximum voltage level nowmay be set equal to about 2.6 volts/cell. Alternatively, if the maximumvoltage level is to be a function of the charge capacity and presentstate-of-charge of battery 10, memory 36 may store data which correlatessuch maximum voltage, charge capacity and state-of-charge levels suchthat the appropriate maximum voltage level, based upon the determinedcharge capacity and state-of-charge, may be retrieved.

Now that the appropriate maximum current and voltage levels have beenselected, the test cycle may be carried out. As the test current changesin successive time steps, as discussed above, A/D converter 34 suppliesCPU 30 with digital representations of corresponding battery voltagelevels. Hence, CPU 30 may obtain the dynamic voltage-currentcharacteristic of the battery during this test cycle. This V-Icharacteristic is compared to the V-I characteristic obtained during theprevious test cycle. In particular, and preferably, abrupt changes ordiscontinuities in the slope of the presently obtained V-Icharacteristics are sensed. Such discontinuities, if any, are comparedto discontinuities which may have been sensed during the preceding testcycle. Inquiry then is made as to whether the presently obtaineddiscontinuities occur at the same test current levels as during thepreceding test cycle. If this inquiry is answered in the affirmative, itis considered that battery 10 has been fully charged and the chargingoperation is terminated. However, if this inquiry is answered in thenegative, the illustrated routine returns to those subroutines wherebythe actual charge capacity, state-of-charge, number of battery cells,and the like are re-determined. It is appreciated that CPU 30 repeatedlyadvances through the program loop illustrated in FIG. 5 until thelast-obtained voltage-current characteristic is substantially identicalto the preceding voltage-current characteristic.

In the preceding discussion, the determination that battery 10 has beenfully charged is based upon sensing that the discontinuities in thevoltage-current characteristics during succeeding test cycles aresubstantially identical. As an alternative, since CPU 30 obtains datarepresenting the entire V-I characteristic, including the hysteresistherein, such digitized versions of the V-I characteristics which areobtained during succeeding test cycles may be compared to each other. Ifsuch comparison is positive, battery 10 is considered to be fullycharged and the charging operation is terminated.

Thus, it is seen that the overall charging operation is carried out in aperiod of time that is dependent upon the actual state-of-charge of thebattery. Contrary to charging devices which have been used heretofore, afixed charging time duration for the overall charging operation is notestablished. Rather, the overall charging duration is variable, and isdependent upon the actual condition of the battery. Furthermore, theoverall charging operation is formed of test and charge cycles which arerepeated, alternately, until the battery is fully charged. During eachcharge cycle, the battery is charged with a ramp voltage whoseparameters are determined by the condition of the battery which isobtained during a preceding test cycle.

FIG. 6 is a waveform diagram of the ramp voltage which is suppliedduring each charge cycle to battery 10 under control of CPU 30. It isseen that successive charge cycles are separated by a test cycle ofsubstantially shorter duration. FIG. 6 does not illustrate either thetest current which is supplied to the battery during each test cycle, orthe voltage which is produced across the battery as a result of thistest current.

From FIG. 6, it is seen that the slope of the ramp voltage may vary.This variation is described above with respect to Table I. Hence, as thevoltage produced across battery 10 reaches predetermined thresholdlevels during different test cycles, the slope of the ramp voltage isreduced accordingly. FIG. 6 also represents the initial or startingvoltage level V_(i) for each ramp voltage. As discussed above, thisstarting voltage V_(i) is a function of the open-circuit voltage ofbattery 10 which is measured during the preceding test cycle. As thisopen-circuit voltage increases, thus representing the state-of-charge ofthe battery, the starting voltage level V_(i) likewise increases. Hence,as the battery becomes more fully charged, the ramp charging voltage ismodified. It is, therefore, seen that the charging operation is"matched" to the condition of the battery.

The subroutine by which CPU 30 is controlled during a test cycle togenerate the current control signal which, in turn, controls poweroutput circuit 18 to supply the aforementioned test current to battery10, now will be described with reference to the flow charts shown inFIGS. 7A and 7B. It will be appreciated that these flow charts serve togenerate a trapezoidal-shaped test current. However, these flow chartsmay be modified so as to result in a triangular test current.

When the program of CPU 30 advances to the test cycle subroutine, theSTART condition illustrated in FIG. 7A is assumed. This subroutine thenis carried out in the following manner: Initially, the current suppliedto battery 10 by power output circuit 18 is read. A digitalrepresentation of this current is supplied to CPU 30 by A/D converter34, as described above. Inquiry then is made as to whether this batterycurrent is greater than the pre-set maximum test current I_(max). Asdescribed above, this maximum current I_(max) is equal to the chargecapacity of the battery (in amp-hours) divided by the factor 2.5. Duringthe initial test cycle, since the actual charge capacity of the batteryis not yet known, i.e. it has not yet been determined, this maximumcurrent level may be set to a substantially lower value. If this inquiryis answered in the affirmative, the subroutine advances to the flowchart shown in FIG. 7B. It is expected that, at the beginning of a testcycle when the test current is substantially equal to zero, this inquirywill be answered in the negative.

Then, inquiry next is made as to whether the test current supplied tobattery 10 exceeds a minimum level. If the test current is too low,i.e., if it is less than this minimum current level, the voltage thenproduced across the battery is not truly responsive to this testcurrent. Hence, it is desirable to ignore the voltage response due tosuch low test current levels. Consequently, if this inquiry is answeredin the negative, any change in the measured battery voltage isdisregarded, thereby ignoring any data which then may be obtainedregarding the slope of the voltage-current characteristic. Nevertheless,even if the test current level is too low, the voltage then producedacross battery 10 is read. Inquiry then is made as to whether thisbattery voltage is greater than a maximum voltage level V_(max). It isrecalled that this maximum voltage level may be preset to be equal toabout 2.6 volts/cell, or may be a function of the charge capacity andcharge level of the battery. During an initial test cycle wherein chargecapacity and charge level have not yet been determined, this maximumvoltage level is set equal to the gas voltage level V_(gas).

It is expected that, during the initial stages of the test cycle, thisinquiry will be answered in the negative. Then, a counter, or register,referred to herein as the C register, is incremented by one count. Thecount of the C register is adapted to be incremented from an initialcount of zero to a maximum count of 255. Each count of the C registermay be decoded and used to generate a test current whose level isdetermined by this decoded count. Thus, as the C register isincremented, the level of the test current correspondingly increases.Conversely, if the count of the C register is decremented, as will bedescribed, the test current level correspondingly is reduced. At thepresent stage of the illustrated subroutine, it is assumed that the Cregister has been incremented from a count of zero to a count of one.Accordingly, after this C register has been incremented, inquiry is madeas to whether the count therein is equal to 255. This inquiry now isanswered in the negative and, after a 16 msec. delay, the subroutinereturns to its START condition. Thereafter, the aforedescribed loop ofthe subroutine is re-executed. It is seen that the C register isincremented by one count every 16 msec. Thus, the C register will beincremented from its initial count of zero to its maximum count of 255in about 4 seconds. Since the test current level is increased inresponse to this incrementing of the C register, it is recognized that,as this register is incremented, the test current exhibits a positiveramp portion whose slope is equal to I_(max) /4 amps per second.

Eventually, the test current level will exceed the aforementionedpredetermined minimum level. At that time, the inquiry as to whether thetest current level exceeds the minimum current level will be answered inthe affirmative, and the subroutine advances to read the batteryvoltage. Inquiry is made as to whether this battery voltage is greaterthan the aforementioned maximum voltage level V_(max). If this inquiryis answered in the affirmative, the subroutine advances to the flowchart shown in FIG. 7B. For the present discussion, it will be assumedthat the battery voltage does not exceed the maximum voltage levelV_(max). Hence, the subroutine advances to store this battery voltage;and then, the preceding stored battery voltage, referred to as V_(old),is subtracted from the present value of the stored battery voltage. Thisdifference between the present battery voltage V and the precedingbattery voltage V_(old) is designated as the change in voltage dV. It isrecognized that this change in voltage dV is attributed to theincremental increase in the test current supplied to the battery.

Inquiry then is made as to whether this change in voltage dV is anegative voltage. During the positive ramp portion of the test current,it is expected that voltage changes dV will be positive. If a negativevoltage change is determined, this change is set equal to zero (dV=0).Then, the change in voltage dV is stored. This stored voltage change dVis either the actual positive voltage change that has been measured or,alternatively, the stored voltage change dV is the zero voltage changewhich has been assumed in the event that the actual voltage change dV isnegative.

It is expected that, as the test current increases in incremental steps,aberrations may be present in the battery voltage that is read inresponse thereto. It is desirable to "smooth" such aberrations. This isattained by storing four successive voltage changes dV and thenaveraging such stored changes to produce an average voltage change ΔV.The dynamic voltage-current characteristic, and particularly the slopeof that V-I characteristic, is determined as a function of the averagevoltage change ΔV that is produced in response to the correspondingchange in current ΔI due to four successive incremental increases in thetest current. In accordance with this averaging feature, after theactual change in voltage dV is stored, inquiry is made as to whetherthis is the fourth occurrence, or measure, of a voltage change. If thisinquiry is answered in the negative, a counter which is provided for thepurpose of determining when four incremental voltage changes have beenmeasured, is incremented. Then, the C register is incremented so as tocorrespondingly increase the level of the test current supplied to thebattery. After the C register has been incremented, inquiry is made asto whether its count is equal to 255. If this inquiry is answered in thenegative, the subroutine returns to its START condition, after a 16msec. delay. Then, the foregoing loop is followed once again.

Ultimately, as the test current level is increased, and as voltagechanges are measured and stored, the fourth incremental voltage changedV will be stored. At that time, the counter which keeps track of thenumber of such voltage changes that have been measured will attain acount of 4. Hence, the inquiry as to whether the fourth voltage changedV has been stored is answered in the affirmative. The voltage-changecounter then will be reset to its initial count of, for example, zero.Then, an average value ΔV of the four stored incremental voltage changesdV will be produced, and this average change in voltage ΔV is stored.

After the average change in voltage ΔV is stored, a representation ofthe slope ΔV/ΔI is produced. It is appreciated that, since the testcurrent is incremented in equal steps, the stored, average change involtage ΔV will, by itself, be a sufficient indication of the slope ofthe dynamic voltage-current characteristic then being obtained for thebattery. Inquiry is made as to whether the latest measure of slope ΔV/ΔIis less than the preceding representation of the slope ΔV/ΔI (old). Ifthis inquiry is answered in the affirmative, that is, if the presentmeasure of the slope of the voltage-current characteristic is less thanthe preceding measure of its slope, the subroutine advances to incrementthe C register, as illustrated, and the subroutine recycles to the loopdiscussed hereinabove. However, if it is determined that the presentmeasure of the slope of the dynamic voltage-current characteristic isequal to or greater than the preceding measure of its slope, the presentmeasure of slope ΔV/ΔI is stored. It is appreciated that this storedmeasure of slope is used, during the next cycle of the illustratedsubroutine, as a measure of the preceding, or "old" measure of slope.

After storing the latest measure of slope ΔV/ΔI, the level of the testcurrent then supplied to the battery which results in this slope of thedynamic voltage-current characteristic also is stored. The subroutinethen advances to increment the C register, and the foregoing process isrepeated.

Thus, it is seen that, during each cycle of the subroutine illustratedin FIG. 7A, the test current is sensed, or read, to determine whether itexceeds the predetermined maximum current level I_(max). Also, thevoltage produced across the battery in response to the test currentlikewise is sensed, or read, to determine if it exceeds thepredetermined maximum voltage level V_(max). In the event that neitherthe maximum current level nor the maximum voltage level is exceeded, thechange in the voltage due to the incremental increase in the testcurrent is obtained, and successive voltage changes dV are averaged toobtain an average change in voltage ΔV. This average change in voltageΔV is combined with the change in test current ΔI so as to derive thedynamic voltage-current characteristic of the tested battery. CPU 30utilizes the data obtained for the dynamic voltage-currentcharacteristic to determine the aforementioned conditions of thebattery, as well as to establish the parameters of the ramp voltagewhich is used during the charge cycle.

Referring now to FIG. 8, it is seen that, as counter C is incrementedwith respect to time (e.g. the count is increased by 1 every 16 msec.),the test current likewise is increased by a predetermined amount. Hence,during successive time steps, the test current is increased by equalincrements, resulting in the positive ramp portion illustrated in FIG.8.

Let it be assumed that, when the positive ramp portion of the testcurrent reaches point a, shown in FIG. 8, the pre-set maximum batterycurrent (or battery voltage) is sensed. In the flow chart shown in FIG.7A, this is indicated by an affirmative answer to the inquiry as towhether the test current is greater than the maximum current levelI_(max), or an affirmative answer to the inquiry as to whether thebattery voltage is greater than the maximum voltage level V_(max). Letit be further assumed that the count then present in register C, at thetime that point a is reached, is less than 255. If the battery currentor voltage exceeds the maximum pre-set current or voltage levels, thesubroutine advances to the flow chart shown in FIG. 7B. According to theillustrated flow chart, the count then present in the C register isloaded into yet another register, designated the E register. It shouldbe appreciated that the contents of the C register are not destroyed atthis time. Then, the test current supplied to the battery is sensed, orread. Inquiry again is made as to whether this test current exceeds thepre-set maximum current level I_(max). If the answer to this inquiry isanswered in the affirmative, the C register is decremented so as tocorrespondingly reduce the test current. It is expected that thisdecrement in the test current will reduce it below the maximum currentlevel I_(max).

If the test current is less than the maximum current level I_(max), orafter the C register has been decremented, as aforesaid, the voltageacross the battery is sensed, or read. Inquiry is made as to whetherthis battery voltage exceeds the pre-set maximum voltage level V_(max).If this inquiry is answered in the affirmative, the C register isdecremented once again so as to correspondingly reduce the test currentsupplied to the battery. It is expected that this further reduction inthe test current will reduce the battery voltage below the maximum levelV_(max). If the battery voltage is less than the maximum voltage levelV_(max), or after the C register has been decremented once again, a 16msec. delay ensues, and then the E register is incremented. Thereafter,inquiry is made as to whether the count of the E register now hasreached the predetermined count of 255. If this inquiry is answered inthe negative, the loop illustrated in FIG. 7B is repeated, wherein thetest current is read, reduced, if necessary, to be below the maximumcurrent level I_(max), the battery voltage is read, reduced, ifnecessary, to bring it below the maximum voltage level V_(max), and theE register is incremented. The broken line extending between points aand b in FIG. 8 illustrates this incrementing of the E register. It isappreciated that, although the E register is incremented, the countpresent in the C register remains fixed. This fixed count corresponds toa constant test current level which is substantially equal to themaximum current level I_(max).

Ultimately, the E register is incremented to a count of 255. At thattime, the inquiry as to whether the count of the E register is equal to255, as illustrated in the aforedescribed loop of FIG. 7B, is answeredin the affirmative. That is, when point b shown in FIG. 8 is reached,this inquiry is answered in the affirmative. Then, the E register isdecremented by 1. Once again, the test current supplied to the batteryis sensed, or read, and this test current is adjusted, if necessary, tobring it just below the maximum current level I_(max). This adjustmentin the current is obtained by decrementing the count then present in theC register.

After reading and, optionally, adjusting the test current level, thevoltage produced across the battery in response to this test current issensed, or read. If this battery voltage exceeds the pre-set maximumvoltage level V_(max), it is adjusted to bring it just below thismaximum voltage level, such as by reducing the test current supplied tothe battery. It is recognized that the test current level is reduced bydecrementing the count of the C register. Then, after reading and,optionally, correcting the battery voltage, a 16 msec. delay ensues; andthen inquiry is made as to whether the count then present in the Eregister is greater than the count present in the C register. If thisinquiry is answered in the affirmative, the aforedescribed loop, bywhich the E register is decremented, is executed once again. The brokenline extending from point b to point c in FIG. 8 represents thisdecrementing of the E register in successive time steps. When point c isreached, the count then present in the E register is equal to the countof the C register. At this time, the inquiry as to whether the contentsof the E register are greater than the contents of the C register isanswered in the negative. Thereafter, the C register is decremented, andthen inquiry is made as to whether the count of the C register is equalto zero. If this inquiry is answered in the negative, a 16 msec. delayensues, and then the C register is decremented once again. Hence, it isrecognized that the C register is decremented in successive time stepsof 16 msecs. duration. As the count of the C register is decremented,the level of the test current is correspondingly reduced by equalincrements. This gradual reduction in the test current in successivetime steps is illustrated by the negative ramp portion, shown by thesolid line in FIG. 8.

Ultimately, the C register is decremented to a count of zero. At thattime, the inquiry as to whether this count is equal to zero is answeredin the affirmative. At that time, the test current is substantiallyequal to zero, and the test cycle terminates.

The charge cycle now may be carried out in the manner describedhereinabove. It is appreciated that, during the preceding test cycle, asdescribed above, voltage and current readings are obtained such that theCPU may obtain the dynamic voltage-current characteristic of the batteryunder test. Also, changes in slope of the V-I characteristic aredetermined, and the test current levels at which such changes aredetected are stored. CPU 30 may compare successive changes in slope tolocate discontinuities in the voltage-current characteristic. Since thetest current levels for each slope measurement are stored, a comparison,during succeeding test cycles, of the locations of discontinuities thusmay be made so as to ascertain when the battery has been charged to itsfully-charged level, as discussed in detail hereinabove.

FIG. 8 is a graphical representation of the manner in which the testcurrent is generated, with respect to time, as the C and E registers areincremented and decremented in successive time steps. It is seen thatthe test current level remains substantially constant for the durationrequired for the E register to be incremented from its initial count,that is, the count which has been loaded thereinto from the C register,to the count of 255, and then to return from this count of 255 to itsinitial count. During this duration, the test current remainssubstantially constant, except for minor adjustments which may be madeto ensure that the battery current and voltage levels do not exceedtheir pre-set maximum levels. That is, although the C register no longeris incremented when the test current reaches its pre-set maximum level,this test current remains at its substantially constant level for theduration equal to the time that would have been needed for the Cregister to reach the count of 255 and then return to the count lastattained thereby. This time duration, that is, the duration over whichthe test current remains substantially constant, is a function of thecount reached by the C register at the time that the test currentreaches its maximum current level I_(max). If the pre-set maximumcurrent level I_(max) is higher than illustrated, the count of the Cregister will be greater when point a is reached, thereby decreasing theduration over which the test current remains substantially constant.Conversely, if the pre-set maximum current level I_(max) is less thanillustrated, the C register will be incremented to a lower count at thetime that point a is reached, thereby increasing the time duration overwhich the test current remains substantially constant. Thus, in thesubroutine described hereinabove, it is appreciated that the test cycleextends for a substantially constant duration, e.g. 8 seconds, with theduration of the constant current level being a function of the pre-setmaximum current level I_(max).

It is appreciated that, while the test current level remains constantfrom point a to point C, the level of this constant current, i.e.I_(max), is sufficient to induce bubbling in the acid of the batterythereby destratifying the electrolyte.

It is appreciated that, if the maximum current level I_(max) is equal toor greater than the current level at which point b is reached, the testcurrent will be substantially triangular in shape. Returning to the flowchart shown in FIG. 7A, the inquiry as to whether the battery current(or voltage) exceeds the pre-set maximum level I_(max) (or V_(max))always will be answered in the negative. Hence, the subroutine shown inFIG. 7A will not advance to that shown in FIG. 7B. Rather, the Cregister will be incremented, with a corresponding incremental increasein the test current, until the count thereof is equal to 255. At thattime, the inquiry as to whether the count of the C register is equal to255 will be answered in the affirmative. Thereafter, following a briefpause, the C register will be decremented in successive time steps. Thisdecrementing will continue until the inquiry as to whether the count ofthe C register is equal to zero is answered in the affirmative. At thattime, the test cycle subroutine terminates.

In the aforementioned operation, it is appreciated that, as the Cregister is incremented, the test current is increased by equalincrements in successive time steps until the point b is reached; andthen the test current is decremented by equal increments in successivetime steps until substantially zero current is reached.

While the present invention has been particularly shown and describedwith reference to certain preferred embodiments thereof, it will bereadily appreciated by those of ordinary skill in the art that variouschanges and modifications in form and details may be made. For example,CPU 30 may, preferably, be formed of a microprocessor, such as an IntelModel 8085 microprocessor. Memory 36 may be comprised of conventionalROM and RAM chips of the type normally utilized with an Intel Model 8085microprocessor. If desired, alternative programmed data processingdevices may be used. It is, therefore, intended that the appended claimsbe interpreted as including such changes and modifications.

What is claimed is:
 1. A method of charging a battery comprising thesteps of (a) testing said battery by supplying energy thereto andmeasuring the voltage thereacross, and deriving therefrom the dynamicvoltage-current characteristic of said battery as a function of thecharge condition thereof; (b) charging said battery by supplying agradually varying voltage thereto, substantially without controlling thecurrent supplied to said battery, for a predetermined time, the rate atwhich said supplied voltage varies being related to said dynamicvoltage-current characteristic obtained in step (a); and (c) repeatingsteps (a) and (b) alternately until the dynamic voltage-currentcharacteristic last obtained is substantially identical to the precedingdynamic voltage-current characteristic, whereupon the charging of saidbattery is terminated.
 2. The method of claim 1 wherein the step ofsupplying energy to said battery comprises supplying a controllablyvarying charging current to said battery; and the voltage producedacross the battery output terminals is measured in response to thecharging current supplied thereto while said charging current is beingsupplied.
 3. The method of claim 2 wherein said step of supplying acontrollably varying charging current comprises generating an increasingramp current followed by a decreasing ramp current; and supplying saidramp currents to said battery.
 4. The method of claim 3 wherein saidstep of supplying a controllably varying charging current furthercomprises sensing when said increasing ramp current attains apredetermined level; maintaining said charging current at saidpredetermined level for a period of time to induce internal bubbling ofsaid battery; and thereafter generating said decreasing ramp current. 5.The method of claim 3 wherein said step of supplying a controllablyvarying charging current further comprises sensing when said voltageproduced across the battery output terminals reaches a predeterminedlevel; maintaining said charging current at the level then attained whensaid voltage reaches said predetermined level for a period of time toinduce internal bubbling of said battery; and thereafter generating saiddecreasing ramp current.
 6. The method of claim 3 wherein said step ofsupplying a controllably varying charging current comprises increasingthe current supplied to said battery by equal increments in successivetime steps; sensing if said current or voltage produced across saidbattery output terminals exceed predetermined current or voltage levels,respectively; if said predetermined current or voltage levels areexceeded, maintaining said current at a substantially constant level forthe duration equal to the time that would have been needed for said timesteps to reach a predetermined number and then return to the step lastattained thereby; and decreasing the current supplied to said battery byequal increments in successive time steps until substantially zerocurrent is supplied.
 7. The method of claim 6 further comprising thesteps of incrementing first counter means with each incremental increasein said current supplied to said battery; loading second counter meanswith the count reached by said first counter means when saidpredetermined current or voltage levels are exceeded; successivelyincrementing said second counter means from the loaded count thereofuntil a predetermined count is reached, and thereafter successivelydecrementing said second counter means until the count thereof is equalto the count of said first counter means; and then decrementing saidfirst counter means with each incremental decrease in said currentsupplied to said battery.
 8. The method of claim 7, further comprisingthe steps of decrementing said current supplied to said battery anddecrementing said first counter means, after said second counter meansis loaded with the count reached by said first counter means, such thatsaid predetermined current and voltage levels are not exceeded.
 9. Themethod of claim 2, wherein said step of deriving the dynamicvoltage-current characteristic includes determining the slope of saidvoltage-current characteristic as a function of the change in themeasured voltage caused by the change in said charging current.
 10. Themethod of claim 2 wherein said step (b) comprises changing the rate atwhich said supplied voltage varies as the charge condition of saidbattery increases.
 11. The method of claim 10 further comprising thesteps of determining the slope of said dynamic voltage-currentcharacteristic in accordance with said measured voltage and suppliedcharging current, thereby indicating the charge capacity of saidbattery; sensing the open-circuit voltage of said battery; and comparingthe sensed open-circuit voltage to reference open-circuit voltage levelsassociated with respective battery charge capacities and therebydetermine the charge condition of said battery.
 12. The method of claim11 wherein said step (b) includes supplying a ramp voltage to saidbattery having one slope until said battery is charged to its gassingcondition, and thereafter supplying said ramp voltage with a secondslope.
 13. The method of claim 12, further comprising the steps ofdetermining the charge capacity of said battery as a function of theobtained dynamic voltage-current characteristic thereof; sensingpredetermined changes in the slope of said obtained dynamicvoltage-current characteristic; and determining that said battery ischarged to its gassing condition when said predetermined changes in saidslope are sensed at a preselected charge condition for saidpredetermined charge capacity.
 14. The method of claim 12 wherein saidgassing condition of said battery is determined by monitoring thecurrent supplied to said battery during charging thereof, and sensingwhen the monitored current begins to decrease.
 15. The method of claim 1further comprising the steps of monitoring the current supplied to saidbattery during charging thereof; and reducing the voltage suppliedthereto if the monitored current exceeds a predetermined current level.16. The method of claim 15 wherein said predetermined current level isdetermined by determining the slope of said dynamic voltage-currentcharacteristic to indicate the charge capacity of said battery, andderiving a predetermined proportion of the indicated charge capacity torepresent said predetermined current level.
 17. The method of claim 1wherein step (c) comprises determining the slope of each dynamicvoltage-current characteristic obtained; sensing abrupt changes in saiddetermined slope; comparing said abrupt changes in the slope of thelast-obtained dynamic voltage-current characteristic to said abruptchanges in the slope of the preceding dynamic voltage-currentcharacteristic; and terminating the charging of said battery if saidabrupt changes occur at substantially the same locations of said dynamicvoltage-current characteristics.
 18. The method of claim 17 wherein saiddynamic voltage-current characteristic is obtained by supplying acontrollably varying charging current to said battery and measuring thevoltage produced across the battery output terminals in response to thecharging current supplied thereto while said charging current is beingsupplied.
 19. The method of claim 18 wherein the location of said abruptchanges in the determined slope of said dynamic voltage-currentcharacteristic is determined by detecting the level of said chargingcurrent supplied to said battery when said abrupt change is sensed. 20.A method of charging a battery comprising the steps of carrying out atest cycle by supplying a controllably varying charging current to saidbattery, measuring the voltage produced across said battery in responseto the charging current supplied thereto while said charging current isbeing supplied, obtaining the dynamic voltage-current characteristic ofsaid battery as a function of the supplied charging current and measuredvoltage, and determining predetermined characteristics of said battery,including the charge capacity, charge condition and selected faults, inaccordance with said dynamic voltage-current characteristic; carryingout a charge cycle for a predetermined time by supplying a ramp voltageto said battery having a slope established in accordance with saiddynamic voltage-current characteristic; and alternately carrying outsaid test and charge cycles until predetermined features of thelast-obtained dynamic voltage-current characteristic are substantiallyidentical to said predetermined features of the preceding dynamicvoltage-current characteristic.
 21. The method of claim 20 wherein saidcharging current is comprised of a gradually increasing portion and agradually decreasing portion; and wherein the dynamic voltage-currentcharacteristics obtained as a function of each said portion exhibitshysteresis.
 22. The method of claim 21 wherein said hysteresis of saiddynamic voltage-current characteristic increases as the charge conditionof said battery increases.
 23. The method of claim 21 wherein saidcharging current is further comprised of a substantially constantportion separating said increasing and decreasing portions so as toinduce bubbling in said battery.
 24. The method of claim 20 wherein saidramp voltage has an initial voltage level determined by the voltagewhich is measured across said battery during said test cycle when saidcharging current is substantially equal to zero.
 25. The method of claim24 wherein the slope of said ramp voltage supplied to said batteryduring said charge cycle is steeper when the charge condition of saidbattery is below the gassing level thereof than when said chargecondition exceeds said gassing level.
 26. The method of claim 25 whereinsaid gassing level is determined by sensing when the voltage which ismeasured across said battery during said test cycle is at least equal toa predetermined gas-voltage level.
 27. The method of claim 26, furthercomprising the step of storing data which correlates battery chargecapacity, charge condition and gas-voltage level; and wherein saidpredetermined gas-voltage level is determined as a function of thedetermined charge capacity and charge condition of said battery.
 28. Themethod of claim 27, wherein said charge capacity is determined as afunction of said voltage which is measured across said battery duringsaid test cycle when said charging current is substantially equal tozero.
 29. The method of claim 27 wherein said battery charge capacity isdetermined by obtaining the slope of said dynamic voltage-currentcharacteristic.
 30. The method of claim 20 wherein said predeterminedfeatures of the dynamic voltage-current characteristic include an abruptchange in the slope thereof, and further comprising the step ofterminating the charge cycle when an abrupt change in the slope of saidlast-obtained dynamic voltage-current characteristic is substantiallyequal to, and occurs at substantially the same location as, an abruptchange in the slope of said preceding dynamic voltage-currentcharacteristic.
 31. The method of claim 20 further comprising the stepof terminating the charge cycle when said last-obtained dynamicvoltage-current characteristic is substantially congruent with saidpreceding dynamic voltage-current characteristic.
 32. Apparatus forcharging a battery comprising energizing means coupled to said batteryto supply energy thereto; sensing means coupled to said battery to sensevoltage thereacross and current thereto; and control means coupled tosaid energizing means and to said sensing means for controlling theenergy supplied to said battery by said energizing means during a testcycle and responsive to at least one of the voltage and current sensedduring said test cycle to obtain the dynamic voltage-currentcharacteristic of said battery and to determine the charge condition ofsaid battery as a function of said dynamic voltage-currentcharacteristic; said control means being operative during a charge cyclefor controlling said energizing means to supply a gradually varyingvoltage to said battery, substantially without controlling the currentsupplied thereto, at a rate related to said dynamic voltage-currentcharacteristic; and said control means being operative to alternatebetween said test cycle and said charge cycle until the latest dynamicvoltage-current characteristic obtained thereby is substantiallyidentical to the preceding dynamic voltage-current characteristic. 33.The apparatus of claim 32 wherein said energizing means comprises meansfor supplying current and voltage to said battery, and said controlmeans controls said energizing means to supply a controllably varyingcharging current to said battery during said test cycle.
 34. Theapparatus of claim 33 wherein said control means is responsive to saidvoltage sensed during said test cycle to obtain said dynamicvoltage-current characteristic of said battery as a function of saidsensed voltage and said supplied charging current.
 35. The apparatus ofclaim 34 wherein said means for supplying current to said batterycomprises current ramp generating means, responsive to said controlmeans, for generating a current ramp which increases with respect totime followed by a current ramp which decreases with respect to time.36. The apparatus of claim 35 wherein said control means is operative tocontrol said current ramp generating means to generate a substantiallyconstant current of predetermined magnitude following said increasingcurrent ramp and preceding said decreasing current ramp.
 37. Theapparatus of claim 36 wherein said constant current magnitude issufficient to induce internal bubbling in said battery.
 38. Theapparatus of claim 33 wherein said control means controls saidenergizing means to reduce the rate at which said voltage is supplied bysaid energizing means to said battery during said charge cycle as thecharge condition of said battery increases.
 39. The apparatus of claim38 wherein said energizing means generates a ramp voltage during saidcharge cycle; and wherein said control means is operative to reduce theslope of said ramp voltage when said sensing means senses that thevoltage produced across said battery during said test cycle exceeds apredetermined gassing voltage.
 40. The apparatus of claim 32 whereinsaid control means comprises programmed data processing means fordetermining said dynamic voltage-current characteristic of said batteryas a function of the voltage sensed by said sensing means and the energysupplied by said energizing means, for determining the charge conditionof said battery as a function of said voltage sensed by said sensingmeans when no energy is supplied to said battery, for varying the rateat which said voltage is supplied to said battery by said energizingmeans as a function of said determined charge condition, and forcomparing successive ones of said determined dynamic voltage-currentcharacteristic to determine when they are substantially identical. 41.Apparatus for charging a battery comprising energizing means coupled tosaid battery to selectively supply current and voltage thereto; sensingmeans coupled to said battery to sense voltage thereacross; and dataprocessing means programmed to alternate repeatedly between a test cycleand a charge cycle and for controlling said energizing means during eachcycle, said data processing means being programmed to control saidenergizing means during a test cycle to supply current to said batteryand being programmed to control said sensing means during a test cycleto sense the voltage across said battery, said data processing meansbeing further programmed during a test cycle to derive the dynamicvoltage-current characteristic of said battery for determining thecharge condition of said battery as a function of the sensed voltage andfor terminating further charge cycles when said data processing meansdetermines the battery to be fully charged.
 42. The apparatus of claim41 wherein said data processing means is programmed to control saidenergizing means during each test cycle to supply a gradually increasingcurrent followed by a gradually decreasing current to said battery. 43.The apparatus of claim 42 wherein said data processing means isprogrammed to further control said energizing means during test cyclesto supply a substantially constant current after said increasing currentreaches a predetermined level, and then followed by said graduallydecreasing current so as to induce internal bubbling in said battery.44. The apparatus of claim 43 wherein said data processing means isprogrammed to determine the charge capacity of said battery as afunction of the voltage sensed during test cycles and to establish saidpredetermined current level as a function of said determined chargecapacity.
 45. The apparatus of claim 42 wherein said data processingmeans is programmed to derive a dynamic voltage-current characteristicas a function of the voltage sensed across said battery and the currentsupplied to said battery during said test cycle.
 46. The apparatus ofclaim 45 wherein said data processing means includes memory means forstoring the derived dynamic voltage-current characteristic; and saiddata processing means is programmed to compare the latest deriveddynamic voltage-current characteristic with the stored preceding dynamicvoltage-current characteristic and to indicate a fully charged conditionwhen the compared dynamic voltage-current characteristics aresubstantially identical.
 47. The apparatus of claim 45 wherein said dataprocessing means is programmed to determine the slope of said deriveddynamic voltage-current characteristic.
 48. The apparatus of claim 47wherein said data processing means is programmed to detect abruptchanges in said slope of the derived dynamic voltage-currentcharacteristic; said data processing means includes memory means forstoring data representing the current level supplied during a test cycleat which said abrupt change in slope occurs; and said data processingmeans is further programmed to indicate a fully charged condition whensubstantially no change is detected in the current level at which saidabrupt change in slope occurs during successive test cycles.
 49. Theapparatus of claim 47 wherein said data processing means is programmedto detect abrupt changes in the slope of said derived dynamicvoltage-current characteristic and to provide an indication of a batteryfault if said abrupt change in slope is detected at a sensed batteryvoltage that is less than a predetermined voltage level.
 50. Theapparatus of claim 49 wherein said predetermined voltage level is thegas-voltage level of said battery.
 51. The apparatus of claim 47 whereinsaid data processing means includes memory means for storing datarepresenting battery charge capacities correlated with different dynamicvoltage-current characteristic slopes; and said data processing means isprogrammed to compare said determined slope with said stored data toobtain an indication of the charge capcity of said battery.
 52. Theapparatus of claim 51 wherein said memory means further stores datarepresenting different charge levels, as a function of battery voltage,associated with each battery charge capacity; and said data processingmeans is programmed to compare the voltage sensed across said batterywhen the current supplied thereto is substantially equal to zero withsaid data representing different charge levels to obtain an indicationof the charge level of said battery.
 53. The apparatus of claim 41wherein said data processing means is programmed to control saidenergizing means during each charge cycle to supply a ramp voltage tosaid battery, said ramp voltage having an initial level and increasingat a controllable rate.
 54. The apparatus of claim 53 wherein said dataprocessing means includes memory means for storing data representingdifferent initial voltage levels correlated with determined batterycharge conditions; and said data processing means is programmed toselect the initial voltage level of said ramp voltage as a function ofthe charge condition of said battery determined during a test cycle. 55.The apparatus of claim 53 wherein said data processing means includesmemory means for storing data representing different ramp voltage ratescorrelated with battery voltages; and said data processing means isprogrammed to select the rate at which said ramp voltage increases as afunction of the voltage sensed across said battery during a test cycle.56. Apparatus for charging a battery comprising energizing means coupledto said battery to selectively supply current and voltage thereto;sensing means coupled to said battery to sense voltage thereacross; anddata processing means programmed to repeatedly establish and alternatebetween a test cycle and a charge cycle and for controlling saidenergizing means during each cycle, said data processing means includingmemory means for storing charge capacity data representing chargecapacities of different batteries, gas voltage data representing the gasvoltage levels of said batteries, charge level data representing thecharge levels of said batteries as a function of the battery voltagethereof, charging voltage data representing predetermined parametersrelating to charging voltages as a function of the battery voltage,maximum current data representing the maximum level of test currents asa function of battery charge capacity, and fault data representingpredetermined battery fault conditions as a function of battery voltage;said data processing means being further programmed to control saidenergizing means during a test cycle to supply a test current havinggradually increasing and decreasing portions and to obtain a dynamicvoltage-current characteristic as a function of said supplied currentand the voltage across said battery sensed by said sensing means whilesaid current is supplied; said data processing means being furtherprogrammed to determine the number of cells included in said battery asa function of said sensed voltage when said current is substantiallyzero; said data processing means being further programmed to determinethe slope of said dynamic voltage-current characteristic and to derivethe charge capacity of said battery as a function of the determinednumber of cells and determined slope; said data processing means beingfurther programmed to compare said sensed voltage when said current issubstantially zero to said stored charge level data to derive the chargelevel of said battery; said data processing means being furtherprogrammed to compare said obtained dynamic voltage-currentcharacteristic to said fault data to indicate the presence of a batteryfault condition; said data processing means being further programmed tocontrol said energizing means during a charge cycle to supply a chargingvoltage to said battery in accordance with said stored charging voltagedata, dependent upon said battery voltage sensed during said test cycle,and said derived charge level of said battery; and said data processingmeans being further programmed to compare the latest dynamicvoltage-current characteristic obtained with the preceding dynamicvoltage-current characteristic and to terminate further charge cycleswhen the compared characteristics are substantially identical.